diff --git a/.github/instructions/struct.instructions.md b/.github/instructions/struct.instructions.md
index 673e135..c92a05c 100644
--- a/.github/instructions/struct.instructions.md
+++ b/.github/instructions/struct.instructions.md
@@ -6,9 +6,9 @@ applyTo: '**'
 
 ## Role
 
-You are an expert assistant that generates valid `.struct.yaml` files for the [StructKit tool](https://github.com/httpdss/structkit), which automates project structure generation from YAML configuration.
+You are an expert assistant that generates valid `.structkit.yaml` files for the [StructKit tool](https://github.com/httpdss/structkit), which automates project structure generation from YAML configuration.
 
-## Defining the `.struct.yaml` file
+## Defining the `.structkit.yaml` file
 
 this file has 3 main keys: `structures`, `folders`, and `variables`.
 
diff --git a/.github/prompts/struct.prompt.md b/.github/prompts/struct.prompt.md
index 941418f..dbb175f 100644
--- a/.github/prompts/struct.prompt.md
+++ b/.github/prompts/struct.prompt.md
@@ -2,9 +2,9 @@
 
 ## Role
 
-You are an expert assistant that generates valid `.struct.yaml` files for the [StructKit tool](https://github.com/httpdss/structkit), which automates project structure generation from YAML configuration.
+You are an expert assistant that generates valid `.structkit.yaml` files for the [StructKit tool](https://github.com/httpdss/structkit), which automates project structure generation from YAML configuration.
 
-## Defining the `.struct.yaml` file
+## Defining the `.structkit.yaml` file
 
 this file has 3 main keys: `structures`, `folders`, and `variables`.
 
diff --git a/.github/workflows/struct-generate.yaml b/.github/workflows/struct-generate.yaml
index 86b55ce..1e7e00d 100644
--- a/.github/workflows/struct-generate.yaml
+++ b/.github/workflows/struct-generate.yaml
@@ -4,10 +4,10 @@ on:
   workflow_call:
     inputs:
       struct_file:
-        description: 'Path to the StructKit file'
+        description: 'Path to the StructKit file. When omitted, uses .structkit.yaml, falling back to .struct.yaml.'
         type: string
         required: false
-        default: '.struct.yaml'
+        default: ''
       output_dir:
         description: 'Path to the output directory'
         type: string
@@ -101,6 +101,17 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ secrets.token }}
         run: |
+          STRUCT_FILE='${{ inputs.struct_file }}'
+          if [ -z "$STRUCT_FILE" ]; then
+            if [ -f .structkit.yaml ]; then
+              STRUCT_FILE=.structkit.yaml
+            elif [ -f .struct.yaml ]; then
+              STRUCT_FILE=.struct.yaml
+            else
+              STRUCT_FILE=.structkit.yaml
+            fi
+          fi
+
           if [ -d ./custom-structures ]; then
 
             structkit list \
@@ -110,7 +121,7 @@ jobs:
               --non-interactive \
               -s ./custom-structures/${{ inputs.custom_structure_path }} \
               ${{ inputs.args }} \
-              ${{ inputs.struct_file }} \
+              "$STRUCT_FILE" \
               ${{ inputs.output_dir }}
           else
             structkit list
@@ -118,7 +129,7 @@ jobs:
             structkit generate \
               --non-interactive \
               ${{ inputs.args }} \
-              ${{ inputs.struct_file }} \
+              "$STRUCT_FILE" \
               ${{ inputs.output_dir }}
           fi
 
diff --git a/.struct.yaml b/.structkit.yaml
similarity index 100%
rename from .struct.yaml
rename to .structkit.yaml
diff --git a/.vscode/settings.json b/.vscode/settings.json
index 80ba861..05afb0d 100644
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@@ -1,6 +1,11 @@
 {
   "yaml.schemas": {
-    "./.vscode/struct-plugins.schema.json": "*.struct.yaml"
+    "./.vscode/struct-plugins.schema.json": [
+      ".structkit.yaml",
+      ".struct.yaml",
+      "*.structkit.yaml",
+      "*.struct.yaml"
+    ]
   },
   "python.languageServer": "None"
 }
diff --git a/README.md b/README.md
index 0432cb4..e43c575 100644
--- a/README.md
+++ b/README.md
@@ -39,7 +39,7 @@ docker run --rm -v "$(pwd):/workdir" ghcr.io/httpdss/structkit:main \
 These are install paths for [StructKit](https://github.com/httpdss/structkit), not separate products. Star this repo.
 
 - [GitHub Action](https://github.com/httpdss/structkit-action) — validate, generate, or drift-check in CI
-- [VS Code / Cursor](https://github.com/httpdss/vscode-structkit) — schema and autocomplete for `.struct.yaml`
+- [VS Code / Cursor](https://github.com/httpdss/vscode-structkit) — schema and autocomplete for `.structkit.yaml`
 - [Agent skills](https://github.com/httpdss/structkit-skills) — inspect, preview, generate, validate from an assistant
 - [pre-commit](https://github.com/httpdss/structkit-pre-commit) — validate structures before they land
 - [Homebrew](https://github.com/httpdss/homebrew-structkit) — `brew tap httpdss/structkit && brew install structkit`
diff --git a/docker-compose.yaml b/docker-compose.yaml
index 1384c38..e5101bb 100644
--- a/docker-compose.yaml
+++ b/docker-compose.yaml
@@ -14,7 +14,7 @@ services:
       "--backup=/app/backup",
       "--file-strategy=rename",
       "--log-file=/app/logfile.log",
-      "/app/examples/python-cli/.struct.yaml",
+      "/app/examples/python-cli/.structkit.yaml",
       "/app/example_project"
     ]
   structkit-test:
@@ -31,6 +31,6 @@ services:
       "--backup=/app/backup",
       "--file-strategy=rename",
       "--log-file=/app/logfile.log",
-      "/app/examples/python-cli/.struct.yaml",
+      "/app/examples/python-cli/.structkit.yaml",
       "/app/example_project"
     ]
diff --git a/docs/agent-skills.md b/docs/agent-skills.md
index fe11d16..5ad2192 100644
--- a/docs/agent-skills.md
+++ b/docs/agent-skills.md
@@ -10,7 +10,7 @@ The [`structkit-workflows`](https://github.com/httpdss/structkit-skills) skill c
 2. Inspect the selected structure and its variables.
 3. Preview or dry-run the generation before writing files.
 4. Use conservative file-conflict behavior for existing repositories.
-5. Validate `.struct.yaml` files and generated output.
+5. Validate `.structkit.yaml` files and generated output.
 
 This is useful when you want an assistant to scaffold from approved StructKit templates instead of inventing project structure from scratch.
 
@@ -33,7 +33,7 @@ hermes skills install https://raw.githubusercontent.com/httpdss/structkit-skills
 Use the skill when an agent needs to:
 
 - Generate a project, Terraform module, CI baseline, documentation bundle, or application scaffold with StructKit.
-- Author or update reusable `.struct.yaml` structures.
+- Author or update reusable `.structkit.yaml` structures.
 - Review a StructKit generation plan before files are written.
 - Package StructKit-backed workflows for repeatable use across repositories.
 
diff --git a/docs/cli-reference.md b/docs/cli-reference.md
index 8affb42..605d250 100644
--- a/docs/cli-reference.md
+++ b/docs/cli-reference.md
@@ -108,10 +108,10 @@ structkit lint [-h] [-l LOG] [-c CONFIG_FILE] [-i LOG_FILE] [-s STRUCTURES_PATH]
 Examples:
 
 ```sh
-structkit lint .struct.yaml
+structkit lint .structkit.yaml
 structkit lint structkit/contribs/project/python.yaml
 structkit lint --all
-structkit lint .struct.yaml --json
+structkit lint .structkit.yaml --json
 ```
 
 ### `generate`
@@ -125,7 +125,7 @@ structkit generate [-h] [-l LOG] [-c CONFIG_FILE] [-i LOG_FILE] [-s STRUCTURES_P
 ```
 
 Defaults when omitted:
-- structure_definition -> .struct.yaml
+- structure_definition -> `.structkit.yaml` (falls back to `.struct.yaml` if the canonical file is missing)
 - base_path -> .
 
 Example:
@@ -135,7 +135,7 @@ structkit generate
 
 **Arguments:**
 
-- `structure_definition` (optional): Path to the YAML configuration file (default: `.struct.yaml`).
+- `structure_definition` (optional): Path to the YAML configuration file (default: `.structkit.yaml`, with a fallback to `.struct.yaml`).
 - `base_path` (optional): Base path where the structure will be created (default: `.`).
 - `-s STRUCTURES_PATH, --structures-path STRUCTURES_PATH`: Path to structure definitions. Can be set via the `STRUCTKIT_STRUCTURES_PATH` environment variable. When using the environment variable (and no explicit CLI flag), an info-level log message will be emitted indicating which path is being used. Takes precedence over named sources.
 - `--source SOURCE`: Named source to use when resolving structure definitions. You can also use `<source>/<structure>` as the structure definition.
@@ -333,7 +333,7 @@ The `config print` command shows the final merged configuration from all layers:
 
 1. Built-in defaults (lowest priority)
 2. User config (`~/.config/struct/config.yaml`)
-3. Project config (`.struct.yaml` or `--config-file`)
+3. Project config (`.structkit.yaml`, legacy `.struct.yaml`, or `--config-file`)
 4. CLI arguments (highest priority)
 
 The command also displays which configuration sources were loaded.
@@ -364,7 +364,7 @@ See the [Configuration](configuration.md) documentation for more details on conf
 
 ### `init`
 
-Initialize a basic .struct.yaml in the target directory.
+Initialize a basic .structkit.yaml in the target directory.
 
 Usage:
 
@@ -372,18 +372,18 @@ Usage:
 structkit init [path]
 ```
 
-- Creates a .struct.yaml if it does not exist.
+- Creates a .structkit.yaml if it does not exist.
 - Includes:
   - pre_hooks/post_hooks with echo commands
   - files with a README.md placeholder
   - folders referencing github/workflows/run-structkit at ./
-- Non-destructive: if .struct.yaml already exists, it is not overwritten and a message is printed.
+- Non-destructive: if `.structkit.yaml` or a legacy `.struct.yaml` already exists, it is not overwritten and a message is printed.
 
 ## Examples
 
 ### Using Defaults
 
-Generate with default structure (.struct.yaml) into current directory:
+Generate with default structure (.structkit.yaml) into current directory:
 
 ```sh
 structkit generate
diff --git a/docs/configuration.md b/docs/configuration.md
index f2eded2..873964c 100644
--- a/docs/configuration.md
+++ b/docs/configuration.md
@@ -6,7 +6,7 @@ Structkit supports a layered configuration system that allows you to set default
 
 1. **Built-in defaults** - Hard-coded defaults that are always present
 2. **User config** - Global defaults from `~/.config/struct/config.yaml`
-3. **Project config** - Project-specific config from `.struct.yaml` or `--config-file`
+3. **Project config** - Project-specific config from `.structkit.yaml` (legacy `.struct.yaml`) or `--config-file`
 4. **CLI arguments** - Command-line flags (highest priority)
 
 ### User Config
@@ -24,7 +24,7 @@ log: WARNING
 
 ### Project Config
 
-Project-specific settings can be defined in a `.struct.yaml` file or specified via the `--config-file` flag. These settings override user config and built-in defaults.
+Project-specific settings can be defined in a `.structkit.yaml` file or specified via the `--config-file` flag. These settings override user config and built-in defaults. A legacy `.struct.yaml` file is still accepted when `.structkit.yaml` is not present.
 
 ### CLI Arguments
 
@@ -80,7 +80,7 @@ The command also displays which configuration sources were used:
 Configuration sources:
   1. Built-in defaults: always loaded
   2. User config: /home/user/.config/struct/config.yaml (exists)
-  3. Project config: .struct.yaml
+  3. Project config: .structkit.yaml
   4. CLI arguments: highest priority
 ```
 
diff --git a/docs/custom-structures.md b/docs/custom-structures.md
index 92147c1..71820c0 100644
--- a/docs/custom-structures.md
+++ b/docs/custom-structures.md
@@ -2,7 +2,7 @@
 
 Let's say you are happy with the default structures that StructKit provides, but you want to customize them for your specific needs. This is totally possible!
 
-The best way to approach this is to have a repository where you can store your custom structures. You can then reference these structures in your `.struct.yaml` files.
+The best way to approach this is to have a repository where you can store your custom structures. You can then reference these structures in your `.structkit.yaml` files.
 
 ## Suggested Repository Structure
 
@@ -18,7 +18,7 @@ structures/
 │   └── structure2.yaml
 ```
 
-This way you could reference your custom structures in your `.struct.yaml` files like this:
+This way you could reference your custom structures in your `.structkit.yaml` files like this:
 
 ```yaml
 folders:
@@ -33,7 +33,7 @@ folders:
 For this to work, you will need to set the path to the custom structures repository using the `-s` option when running StructKit:
 
 ```sh
-structkit generate -s ~/path/to/custom-structures/structures file://.struct.yaml ./output
+structkit generate -s ~/path/to/custom-structures/structures file://.structkit.yaml ./output
 ```
 
 ## Named custom sources
@@ -64,7 +64,7 @@ Git-backed sources are cloned into `$XDG_CACHE_HOME/structkit/sources` or `~/.ca
 
 ## File-local sources
 
-Committed `.struct.yaml` files can declare their own named sources. This keeps generation portable and protects existing files from changes to a user's global `structkit sources` configuration.
+Committed `.structkit.yaml` files can declare their own named sources. This keeps generation portable and protects existing files from changes to a user's global `structkit sources` configuration. Legacy `.struct.yaml` files are still read when `.structkit.yaml` is not present.
 
 ```yaml
 sources:
@@ -104,7 +104,7 @@ folders:
       struct: github://httpdss/platform-structures@v1.2.0/structures/python/service
 ```
 
-For reproducible `.struct.yaml` files, prefer tags or commit SHAs over mutable branches.
+For reproducible `.structkit.yaml` files, prefer tags or commit SHAs over mutable branches.
 
 Use a source explicitly with `--source`:
 
diff --git a/docs/examples/index.md b/docs/examples/index.md
index 42351c9..1bf657a 100644
--- a/docs/examples/index.md
+++ b/docs/examples/index.md
@@ -6,11 +6,11 @@ StructKit's polished examples live in the repository-level [`examples/`](../../e
 
 | Example | Use case | Source |
 |---|---|---|
-| Python CLI | Small Python command-line tool with tests and package metadata | [`examples/python-cli/.struct.yaml`](../../examples/python-cli/.struct.yaml) |
-| FastAPI service | API service with tests, Dockerfile, and environment example | [`examples/fastapi-service/.struct.yaml`](../../examples/fastapi-service/.struct.yaml) |
-| Terraform module | Reusable infrastructure module skeleton | [`examples/terraform-module/.struct.yaml`](../../examples/terraform-module/.struct.yaml) |
-| GitHub Actions CI baseline | Standard Python CI workflow and pre-commit setup | [`examples/github-actions-ci/.struct.yaml`](../../examples/github-actions-ci/.struct.yaml) |
-| AI agent / MCP scaffold | Agent-friendly repository structure and instructions | [`examples/ai-agent-mcp/.struct.yaml`](../../examples/ai-agent-mcp/.struct.yaml) |
+| Python CLI | Small Python command-line tool with tests and package metadata | [`examples/python-cli/.structkit.yaml`](../../examples/python-cli/.structkit.yaml) |
+| FastAPI service | API service with tests, Dockerfile, and environment example | [`examples/fastapi-service/.structkit.yaml`](../../examples/fastapi-service/.structkit.yaml) |
+| Terraform module | Reusable infrastructure module skeleton | [`examples/terraform-module/.structkit.yaml`](../../examples/terraform-module/.structkit.yaml) |
+| GitHub Actions CI baseline | Standard Python CI workflow and pre-commit setup | [`examples/github-actions-ci/.structkit.yaml`](../../examples/github-actions-ci/.structkit.yaml) |
+| AI agent / MCP scaffold | Agent-friendly repository structure and instructions | [`examples/ai-agent-mcp/.structkit.yaml`](../../examples/ai-agent-mcp/.structkit.yaml) |
 
 Start with the [examples index](../../examples/README.md) for copy-paste commands, expected output, and customization notes.
 
@@ -19,7 +19,7 @@ Start with the [examples index](../../examples/README.md) for copy-paste command
 Every example can be previewed with `--dry-run --diff`:
 
 ```bash
-structkit generate --vars "project_name=DemoCLI,package_name=demo_cli,cli_command=demo-cli,description=A small Python CLI generated by StructKit." examples/python-cli/.struct.yaml /tmp/structkit-python-cli-demo --dry-run --diff
+structkit generate --vars "project_name=DemoCLI,package_name=demo_cli,cli_command=demo-cli,description=A small Python CLI generated by StructKit." examples/python-cli/.structkit.yaml /tmp/structkit-python-cli-demo --dry-run --diff
 ```
 
 Then remove `--dry-run --diff` when you're ready to write files.
diff --git a/docs/github-integration.md b/docs/github-integration.md
index 64d5e49..089f955 100644
--- a/docs/github-integration.md
+++ b/docs/github-integration.md
@@ -21,6 +21,8 @@ jobs:
       token: ${{ secrets.STRUCT_RUN_TOKEN }}
 ```
 
+When `struct_file` is omitted, the workflow uses `.structkit.yaml` if present and falls back to a legacy `.struct.yaml`.
+
 ## Best Practices
 
 1. **Secure Your Token**: Store GitHub tokens in secrets management tools.
diff --git a/docs/hooks.md b/docs/hooks.md
index 0c2ebc3..0621ccf 100644
--- a/docs/hooks.md
+++ b/docs/hooks.md
@@ -187,11 +187,11 @@ You can disable hooks entirely using the `--no-hooks` flag or environment variab
 
 ```bash
 # Using CLI flag
-structkit generate .struct.yaml --no-hooks
+structkit generate .structkit.yaml --no-hooks
 
 # Using environment variable
 export STRUCTKIT_NO_HOOKS=true
-structkit generate .struct.yaml
+structkit generate .structkit.yaml
 ```
 
 This is recommended for:
@@ -204,7 +204,7 @@ This is recommended for:
 By default, StructKit prompts for confirmation before running hooks in interactive mode:
 
 ```bash
-$ structkit generate .struct.yaml
+$ structkit generate .structkit.yaml
 
 ⚠️  The following pre-hooks will be executed:
   - echo "Preparing environment..."
@@ -243,11 +243,11 @@ When an allowlist exists:
 You can also specify a custom allowlist path:
 
 ```bash
-structkit generate .struct.yaml --hooks-allowlist /path/to/allowlist.txt
+structkit generate .structkit.yaml --hooks-allowlist /path/to/allowlist.txt
 
 # Or via environment variable
 export STRUCTKIT_HOOKS_ALLOWLIST=/path/to/allowlist.txt
-structkit generate .struct.yaml
+structkit generate .structkit.yaml
 ```
 
 ### MCP Integration Safety
@@ -301,7 +301,7 @@ post_hooks:
 ### Safe Hook Example with Allowlist
 
 ```yaml
-# .struct.yaml
+# .structkit.yaml
 pre_hooks:
   - echo "Preparing environment..."
   - python -c "import sys; print(sys.version)"
diff --git a/docs/installation.md b/docs/installation.md
index 1ce3011..81aa831 100644
--- a/docs/installation.md
+++ b/docs/installation.md
@@ -25,7 +25,7 @@ Clone the repository and install locally. See the [Development](development.md)
 Run StructKit without installing, using Docker:
 
 ```sh
-docker run -v $(pwd):/workdir -u $(id -u):$(id -g) ghcr.io/httpdss/structkit:main generate file:///workdir/examples/python-cli/.struct.yaml /workdir/example_output
+docker run -v $(pwd):/workdir -u $(id -u):$(id -g) ghcr.io/httpdss/structkit:main generate file:///workdir/examples/python-cli/.structkit.yaml /workdir/example_output
 ```
 
 Refer to the [Quick Start](quickstart.md) guide for more options.
diff --git a/docs/mcp-integration.md b/docs/mcp-integration.md
index 2f845de..186ebd1 100644
--- a/docs/mcp-integration.md
+++ b/docs/mcp-integration.md
@@ -113,7 +113,7 @@ Lint one or more structure YAML files or structure names for quality and safety
 {
   "name": "lint_structure",
   "arguments": {
-    "targets": ["project/python", "/path/to/.struct.yaml"],
+    "targets": ["project/python", "/path/to/.structkit.yaml"],
     "structures_path": "/path/to/custom/structures",
     "lint_all": false,
     "output": "json"
diff --git a/docs/quickstart.md b/docs/quickstart.md
index fe9198e..f03c9d2 100644
--- a/docs/quickstart.md
+++ b/docs/quickstart.md
@@ -17,7 +17,7 @@ docker run \
   -v $(pwd):/workdir \
   -u $(id -u):$(id -g) \
   ghcr.io/httpdss/structkit:main generate \
-  file:///workdir/examples/python-cli/.struct.yaml \
+  file:///workdir/examples/python-cli/.structkit.yaml \
   /workdir/example_output
 ```
 
@@ -28,7 +28,7 @@ docker run \
   -v $(pwd):/workdir \
   -u $(id -u):$(id -g) \
   ghcr.io/httpdss/structkit:alpine generate \
-  file:///workdir/examples/python-cli/.struct.yaml \
+  file:///workdir/examples/python-cli/.structkit.yaml \
   /workdir/example_output
 ```
 
@@ -50,7 +50,7 @@ vim structure.yaml # or copy one of the examples from the examples/ directory
 structkit generate structure.yaml .
 ```
 
-> Note: The `file://` protocol is automatically added for `.yaml` files, so `structure.yaml` and `file://structure.yaml` work identically. Additionally, if your file is named `.struct.yaml` in the current directory and you want to generate into the current directory, you can just run `structkit generate`.
+> Note: The `file://` protocol is automatically added for `.yaml` files, so `structure.yaml` and `file://structure.yaml` work identically. Additionally, if your file is named `.structkit.yaml` in the current directory (or the legacy `.struct.yaml`) and you want to generate into the current directory, you can just run `structkit generate`.
 
 ## Discovering Available Structures
 
@@ -83,13 +83,13 @@ structkit generate project/nodejs ./my-node-app
 
 ## Bootstrap a new project
 
-Start with a minimal .struct.yaml:
+Start with a minimal .structkit.yaml:
 
 ```sh
 structkit init
 ```
 
-This writes a basic .struct.yaml with hooks, a README, and a reference to the run-structkit workflow.
+This writes a basic .structkit.yaml with hooks, a README, and a reference to the run-structkit workflow.
 
 ## Next Steps
 
diff --git a/docs/schema.md b/docs/schema.md
index 3d1a24e..7631cfb 100644
--- a/docs/schema.md
+++ b/docs/schema.md
@@ -20,19 +20,24 @@ https://raw.githubusercontent.com/httpdss/structkit/main/struct-schema.json
 ```json
 {
   "yaml.schemas": {
-    "https://raw.githubusercontent.com/httpdss/structkit/main/struct-schema.json": ".struct.yaml"
+    "https://raw.githubusercontent.com/httpdss/structkit/main/struct-schema.json": [
+      ".structkit.yaml",
+      ".struct.yaml",
+      "*.structkit.yaml",
+      "*.struct.yaml"
+    ]
   }
 }
 ```
 
-This provides validation and autocompletion for all `.struct.yaml` files.
+This provides validation and autocompletion for `.structkit.yaml` files. Legacy `.struct.yaml` files are included for compatibility.
 
 ### JetBrains IDEs (IntelliJ, PyCharm, etc.)
 
 1. Go to **Settings** → **Languages & Frameworks** → **Schemas and DTDs** → **JSON Schema Mappings**
 2. Click **+** to add a new mapping
 3. Set **Schema file or URL** to: `https://raw.githubusercontent.com/httpdss/structkit/main/struct-schema.json`
-4. Set **File path pattern** to: `*.struct.yaml`
+4. Set **File path pattern** to: `*.structkit.yaml` (also add `*.struct.yaml` if you still use the legacy name)
 
 ## Generating Custom Schema
 
@@ -45,7 +50,7 @@ structkit generate-schema -s /path/to/custom/structures -o my-schema.json
 # Use in VS Code settings
 {
   "yaml.schemas": {
-    "./my-schema.json": ".struct.yaml"
+    "./my-schema.json": [".structkit.yaml", ".struct.yaml"]
   }
 }
 ```
diff --git a/docs/usage.md b/docs/usage.md
index 635e2cf..e018e57 100644
--- a/docs/usage.md
+++ b/docs/usage.md
@@ -36,12 +36,14 @@ structkit generate <Tab>
 
 ### Using Defaults
 
-If you have a .struct.yaml in the current directory and want to generate into the current directory, you can simply run:
+If you have a `.structkit.yaml` in the current directory and want to generate into the current directory, you can simply run:
 
 ```sh
 structkit generate
 ```
 
+The canonical project file is `.structkit.yaml`. If that file is missing, `structkit generate` still reads a legacy `.struct.yaml` in the same directory. If both exist, `.structkit.yaml` is used.
+
 ### Simple Example
 
 ```sh
@@ -58,7 +60,7 @@ structkit generate my-config.yaml ./output
 structkit generate file://my-config.yaml ./output
 ```
 
-Tip: If your config file is named `.struct.yaml` in the current directory and you want to generate into the current directory, you can simply run:
+Tip: If your config file is named `.structkit.yaml` (or legacy `.struct.yaml`) in the current directory and you want to generate into the current directory, you can simply run:
 
 ```sh
 structkit generate
@@ -120,15 +122,15 @@ structkit generate-schema -s /path/to/custom/structures -o schema.json
 
 The generated schema includes all available structures from both the built-in contribs directory and any custom structures path you specify. This is useful for:
 
-- IDE autocompletion when writing `.struct.yaml` files
+- IDE autocompletion when writing `.structkit.yaml` files
 - Validation of structure references in your configurations
 - Programmatic discovery of available templates
 
 ## Other Commands
 
-### Initialize a project with .struct.yaml
+### Initialize a project with .structkit.yaml
 
-Create a minimal .struct.yaml in the current directory:
+Create a minimal .structkit.yaml in the current directory:
 
 ```sh
 structkit init
diff --git a/docs/vhs/README.md b/docs/vhs/README.md
index 1e5864e..41a32bd 100644
--- a/docs/vhs/README.md
+++ b/docs/vhs/README.md
@@ -355,7 +355,7 @@ Type "echo && echo 'Available structures in schema:' && jq -r '.definitions.Plug
 Sleep 5
 Type "" Enter
 Type "# Schema can be used in VS Code for autocompletion" Enter
-Type "echo 'Add to your .struct.yaml files for IDE support:'" Enter
+Type "echo 'Add to your .structkit.yaml files for IDE support:'" Enter
 Type "echo '# yaml-language-server: \$schema=./struct-schema.json'" Enter
 Sleep 3
 ```
diff --git a/docs/vhs/schema-generation.tape b/docs/vhs/schema-generation.tape
index 127f2a4..2f15b4a 100644
--- a/docs/vhs/schema-generation.tape
+++ b/docs/vhs/schema-generation.tape
@@ -44,7 +44,7 @@ Type "{"
 Enter
 Type '  "yaml.schemas": {'
 Enter
-Type '    "./.vscode/struct-plugins.schema.json": "*.struct.yaml"'
+Type '    "./.vscode/struct-plugins.schema.json": "*.structkit.yaml"'
 Enter
 Type "  }"
 Enter
@@ -56,7 +56,7 @@ Sleep 2s
 
 Type "# Now VSCode will provide autocompletion for structkit names!"
 Enter
-Type "# when you type 'struct:' in a .struct.yaml file"
+Type "# when you type 'struct:' in a .structkit.yaml file"
 Enter
 Sleep 2s
 
diff --git a/examples/README.md b/examples/README.md
index 33b92df..d59f588 100644
--- a/examples/README.md
+++ b/examples/README.md
@@ -6,19 +6,19 @@ This directory contains polished, copy-pasteable StructKit examples for common d
 
 | Example | Best for | Command |
 |---|---|---|
-| [Python CLI](python-cli/) | Packaging a small Python command-line tool | `structkit generate --vars "project_name=DemoCLI,package_name=demo_cli,cli_command=demo-cli,description=A small Python CLI generated by StructKit." examples/python-cli/.struct.yaml ./demo-python-cli` |
-| [FastAPI service](fastapi-service/) | Bootstrapping an API service with tests and Docker | `structkit generate --vars "service_name=DemoAPI,module_name=app,description=A small FastAPI service generated by StructKit." examples/fastapi-service/.struct.yaml ./demo-fastapi-service` |
-| [Terraform module](terraform-module/) | Creating a reusable infrastructure module skeleton | `structkit generate --vars "module_name=terraform-example-module,description=A reusable Terraform module generated by StructKit.,terraform_version=1.6.0,provider_source=hashicorp/null,provider_version=>= 3.2.0" examples/terraform-module/.struct.yaml ./demo-terraform-module` |
-| [GitHub Actions CI baseline](github-actions-ci/) | Adding a standard Python CI workflow to a repo | `structkit generate --vars "project_name=DemoPythonProject,python_version=3.12" examples/github-actions-ci/.struct.yaml ./demo-ci-baseline` |
-| [AI agent / MCP scaffold](ai-agent-mcp/) | Giving AI coding assistants a project structure and instructions | `structkit generate --vars "project_name=AI Assisted Project,description=A project scaffolded for AI-assisted development with StructKit." examples/ai-agent-mcp/.struct.yaml ./demo-ai-agent-project` |
-| [Versioned sources](versioned-sources/) | Pinning reusable struct sources and inheriting the same source in nested structs | `structkit generate examples/versioned-sources/.struct.yaml ./demo-versioned-sources` |
+| [Python CLI](python-cli/) | Packaging a small Python command-line tool | `structkit generate --vars "project_name=DemoCLI,package_name=demo_cli,cli_command=demo-cli,description=A small Python CLI generated by StructKit." examples/python-cli/.structkit.yaml ./demo-python-cli` |
+| [FastAPI service](fastapi-service/) | Bootstrapping an API service with tests and Docker | `structkit generate --vars "service_name=DemoAPI,module_name=app,description=A small FastAPI service generated by StructKit." examples/fastapi-service/.structkit.yaml ./demo-fastapi-service` |
+| [Terraform module](terraform-module/) | Creating a reusable infrastructure module skeleton | `structkit generate --vars "module_name=terraform-example-module,description=A reusable Terraform module generated by StructKit.,terraform_version=1.6.0,provider_source=hashicorp/null,provider_version=>= 3.2.0" examples/terraform-module/.structkit.yaml ./demo-terraform-module` |
+| [GitHub Actions CI baseline](github-actions-ci/) | Adding a standard Python CI workflow to a repo | `structkit generate --vars "project_name=DemoPythonProject,python_version=3.12" examples/github-actions-ci/.structkit.yaml ./demo-ci-baseline` |
+| [AI agent / MCP scaffold](ai-agent-mcp/) | Giving AI coding assistants a project structure and instructions | `structkit generate --vars "project_name=AI Assisted Project,description=A project scaffolded for AI-assisted development with StructKit." examples/ai-agent-mcp/.structkit.yaml ./demo-ai-agent-project` |
+| [Versioned sources](versioned-sources/) | Pinning reusable struct sources and inheriting the same source in nested structs | `structkit generate examples/versioned-sources/.structkit.yaml ./demo-versioned-sources` |
 
 ## How to run an example
 
 From the repository root:
 
 ```bash
-structkit generate --vars "project_name=DemoCLI,package_name=demo_cli,cli_command=demo-cli,description=A small Python CLI generated by StructKit." examples/python-cli/.struct.yaml /tmp/structkit-python-cli-demo
+structkit generate --vars "project_name=DemoCLI,package_name=demo_cli,cli_command=demo-cli,description=A small Python CLI generated by StructKit." examples/python-cli/.structkit.yaml /tmp/structkit-python-cli-demo
 ```
 
 Most examples include defaults for variables. Pass `--vars` when you want a non-interactive, copy-pasteable command with a specific project name or package name:
@@ -26,14 +26,14 @@ Most examples include defaults for variables. Pass `--vars` when you want a non-
 ```bash
 structkit generate \
   --vars "project_name=DemoCLI,package_name=demo_cli,cli_command=demo-cli,description=A small Python CLI generated by StructKit." \
-  examples/python-cli/.struct.yaml \
+  examples/python-cli/.structkit.yaml \
   /tmp/demo-cli
 ```
 
 Use `--dry-run --diff` to preview output before writing files:
 
 ```bash
-structkit generate --vars "service_name=DemoAPI,module_name=app,description=A small FastAPI service generated by StructKit." examples/fastapi-service/.struct.yaml /tmp/demo-api --dry-run --diff
+structkit generate --vars "service_name=DemoAPI,module_name=app,description=A small FastAPI service generated by StructKit." examples/fastapi-service/.structkit.yaml /tmp/demo-api --dry-run --diff
 ```
 
 ## Notes for contributors
diff --git a/examples/ai-agent-mcp/.struct.yaml b/examples/ai-agent-mcp/.structkit.yaml
similarity index 95%
rename from examples/ai-agent-mcp/.struct.yaml
rename to examples/ai-agent-mcp/.structkit.yaml
index ede5e3b..05e5cb8 100644
--- a/examples/ai-agent-mcp/.struct.yaml
+++ b/examples/ai-agent-mcp/.structkit.yaml
@@ -25,9 +25,9 @@ files:
 
         ```bash
         # Replace with project-specific checks
-        structkit validate .struct.yaml
+        structkit validate .structkit.yaml
         ```
-  - .struct.yaml:
+  - .structkit.yaml:
       content: |
         files:
           - README.md:
@@ -84,7 +84,7 @@ files:
 
         - [ ] Replace generated placeholders with project-specific content.
         - [ ] Add canonical build and test commands to `AGENTS.md`.
-        - [ ] Validate `.struct.yaml` after customizing it.
+        - [ ] Validate `.structkit.yaml` after customizing it.
 variables:
   - project_name:
       description: "Project name."
diff --git a/examples/ai-agent-mcp/README.md b/examples/ai-agent-mcp/README.md
index da9e2aa..43a17f6 100644
--- a/examples/ai-agent-mcp/README.md
+++ b/examples/ai-agent-mcp/README.md
@@ -9,19 +9,19 @@ Use this when creating a repo that will be edited by AI coding assistants and yo
 ## Command
 
 ```bash
-structkit generate --vars "project_name=AI Assisted Project,description=A project scaffolded for AI-assisted development with StructKit." examples/ai-agent-mcp/.struct.yaml ./demo-ai-agent-project
+structkit generate --vars "project_name=AI Assisted Project,description=A project scaffolded for AI-assisted development with StructKit." examples/ai-agent-mcp/.structkit.yaml ./demo-ai-agent-project
 ```
 
 ## Expected output
 
 - `README.md`
 - `AGENTS.md`
-- `.struct.yaml`
+- `.structkit.yaml`
 - `docs/architecture.md`
 - `docs/decisions/0001-record-architecture-decisions.md`
 - `tasks/backlog.md`
 
 ## Customization notes
 
-- Commit the generated `.struct.yaml` so humans and AI agents can regenerate the agreed structure.
+- Commit the generated `.structkit.yaml` so humans and AI agents can regenerate the agreed structure.
 - Adapt `AGENTS.md` with repository-specific build, test, and review commands.
diff --git a/examples/config-layering/README.md b/examples/config-layering/README.md
index 7737ac5..d584d08 100644
--- a/examples/config-layering/README.md
+++ b/examples/config-layering/README.md
@@ -8,7 +8,7 @@ Structkit supports configuration at four levels (from lowest to highest priority
 
 1. **Built-in defaults** - Hard-coded baseline values
 2. **User config** - Global defaults from `~/.config/struct/config.yaml`
-3. **Project config** - Project-specific config from `.struct.yaml` or `--config-file`
+3. **Project config** - Project-specific config from `.structkit.yaml` (legacy `.struct.yaml`) or `--config-file`
 4. **CLI arguments** - Command-line flags (highest priority)
 
 ## Setup
@@ -138,7 +138,7 @@ backup: ~/structkit-backups
 
 Share project-specific settings in version control:
 ```yaml
-# .struct.yaml (checked into git)
+# .structkit.yaml (checked into git)
 structures_path: ./team-structures
 input_store: ./.structkit/input.json
 non_interactive: true
diff --git a/examples/config-layering/project-config-example.yaml b/examples/config-layering/project-config-example.yaml
index d52cde2..0cdc744 100644
--- a/examples/config-layering/project-config-example.yaml
+++ b/examples/config-layering/project-config-example.yaml
@@ -1,7 +1,7 @@
 # Example project config file
 #
 # This file can be checked into version control to share project-specific
-# settings with your team. Use with --config-file or as .struct.yaml
+# settings with your team. Use with --config-file or as .structkit.yaml
 
 # Project-specific structures location
 structures_path: ./custom-structures
diff --git a/examples/fastapi-service/.struct.yaml b/examples/fastapi-service/.structkit.yaml
similarity index 100%
rename from examples/fastapi-service/.struct.yaml
rename to examples/fastapi-service/.structkit.yaml
diff --git a/examples/fastapi-service/README.md b/examples/fastapi-service/README.md
index 208622f..1b00b75 100644
--- a/examples/fastapi-service/README.md
+++ b/examples/fastapi-service/README.md
@@ -9,7 +9,7 @@ Use this when starting a small internal API, service prototype, or baseline for
 ## Command
 
 ```bash
-structkit generate --vars "service_name=DemoAPI,module_name=app,description=A small FastAPI service generated by StructKit." examples/fastapi-service/.struct.yaml ./demo-fastapi-service
+structkit generate --vars "service_name=DemoAPI,module_name=app,description=A small FastAPI service generated by StructKit." examples/fastapi-service/.structkit.yaml ./demo-fastapi-service
 ```
 
 ## Expected output
diff --git a/examples/github-actions-ci/.struct.yaml b/examples/github-actions-ci/.structkit.yaml
similarity index 100%
rename from examples/github-actions-ci/.struct.yaml
rename to examples/github-actions-ci/.structkit.yaml
diff --git a/examples/github-actions-ci/README.md b/examples/github-actions-ci/README.md
index cc4edfd..4a5e562 100644
--- a/examples/github-actions-ci/README.md
+++ b/examples/github-actions-ci/README.md
@@ -9,7 +9,7 @@ Use this when you want to apply a consistent CI baseline across internal Python
 ## Command
 
 ```bash
-structkit generate --vars "project_name=DemoPythonProject,python_version=3.12" examples/github-actions-ci/.struct.yaml ./demo-ci-baseline
+structkit generate --vars "project_name=DemoPythonProject,python_version=3.12" examples/github-actions-ci/.structkit.yaml ./demo-ci-baseline
 ```
 
 ## Expected output
diff --git a/examples/python-cli/.struct.yaml b/examples/python-cli/.structkit.yaml
similarity index 100%
rename from examples/python-cli/.struct.yaml
rename to examples/python-cli/.structkit.yaml
diff --git a/examples/python-cli/README.md b/examples/python-cli/README.md
index 76c8965..bd99392 100644
--- a/examples/python-cli/README.md
+++ b/examples/python-cli/README.md
@@ -9,7 +9,7 @@ Use this when you want a quick starting point for an internal automation CLI, de
 ## Command
 
 ```bash
-structkit generate --vars "project_name=DemoCLI,package_name=demo_cli,cli_command=demo-cli,description=A small Python CLI generated by StructKit." examples/python-cli/.struct.yaml ./demo-python-cli
+structkit generate --vars "project_name=DemoCLI,package_name=demo_cli,cli_command=demo-cli,description=A small Python CLI generated by StructKit." examples/python-cli/.structkit.yaml ./demo-python-cli
 ```
 
 Optional custom values:
@@ -19,7 +19,7 @@ structkit generate \
   --var project_name=ReleaseHelper \
   --var package_name=release_helper \
   --var cli_command=release-helper \
-  examples/python-cli/.struct.yaml \
+  examples/python-cli/.structkit.yaml \
   ./release-helper
 ```
 
diff --git a/examples/terraform-module/.struct.yaml b/examples/terraform-module/.structkit.yaml
similarity index 100%
rename from examples/terraform-module/.struct.yaml
rename to examples/terraform-module/.structkit.yaml
diff --git a/examples/terraform-module/README.md b/examples/terraform-module/README.md
index 0648ea5..4ad5e17 100644
--- a/examples/terraform-module/README.md
+++ b/examples/terraform-module/README.md
@@ -9,7 +9,7 @@ Use this when starting an infrastructure module that should have consistent vari
 ## Command
 
 ```bash
-structkit generate --vars "module_name=terraform-example-module,description=A reusable Terraform module generated by StructKit.,terraform_version=1.6.0,provider_source=hashicorp/null,provider_version=>= 3.2.0" examples/terraform-module/.struct.yaml ./demo-terraform-module
+structkit generate --vars "module_name=terraform-example-module,description=A reusable Terraform module generated by StructKit.,terraform_version=1.6.0,provider_source=hashicorp/null,provider_version=>= 3.2.0" examples/terraform-module/.structkit.yaml ./demo-terraform-module
 ```
 
 ## Expected output
diff --git a/examples/versioned-sources/.struct.yaml b/examples/versioned-sources/.structkit.yaml
similarity index 100%
rename from examples/versioned-sources/.struct.yaml
rename to examples/versioned-sources/.structkit.yaml
diff --git a/examples/versioned-sources/README.md b/examples/versioned-sources/README.md
index 308bdf6..f9f76a7 100644
--- a/examples/versioned-sources/README.md
+++ b/examples/versioned-sources/README.md
@@ -1,6 +1,6 @@
 # Versioned Sources Example
 
-This example shows how a committed `.struct.yaml` can define its own named source and then reference structs from that source.
+This example shows how a committed `.structkit.yaml` can define its own named source and then reference structs from that source.
 
 The example uses a local source so it works offline:
 
@@ -31,14 +31,14 @@ sources:
 - `platform/app/base` resolves through the file-local `platform` source.
 - `app/base.yaml` references `app/ci` without a source prefix.
 - The nested `app/ci` reference inherits the same `platform` source context.
-- A future change to the user's global `structkit sources` config will not affect this `.struct.yaml` file.
+- A future change to the user's global `structkit sources` config will not affect this `.structkit.yaml` file.
 
 ## Run it
 
 From the StructKit repository root:
 
 ```bash
-structkit generate examples/versioned-sources/.struct.yaml /tmp/structkit-versioned-sources-demo
+structkit generate examples/versioned-sources/.structkit.yaml /tmp/structkit-versioned-sources-demo
 ```
 
 Expected generated files:
@@ -52,5 +52,5 @@ Expected generated files:
 Preview without writing files:
 
 ```bash
-structkit generate examples/versioned-sources/.struct.yaml /tmp/structkit-versioned-sources-demo --dry-run --diff
+structkit generate examples/versioned-sources/.structkit.yaml /tmp/structkit-versioned-sources-demo --dry-run --diff
 ```
diff --git a/structkit/commands/generate.py b/structkit/commands/generate.py
index 16b3865..8961e38 100644
--- a/structkit/commands/generate.py
+++ b/structkit/commands/generate.py
@@ -8,6 +8,11 @@
 from structkit.sources import SourceError, resolve_structures_path
 from structkit.struct_refs import SourceContext, resolve_struct_reference
 from structkit.input_store import InputStoreError
+from structkit.project_file import (
+    CANONICAL_PROJECT_STRUCT_FILE,
+    LEGACY_PROJECT_STRUCT_FILE,
+    resolve_project_struct_file,
+)
 
 import subprocess
 
@@ -21,7 +26,16 @@ class GenerateCommand(Command):
   def __init__(self, parser):
     super().__init__(parser)
     parser.description = "Generate the project structure from a YAML configuration file"
-    structure_arg = parser.add_argument('structure_definition', nargs='?', default='.struct.yaml', type=str, help='Path to the YAML configuration file (default: .struct.yaml)')
+    structure_arg = parser.add_argument(
+      'structure_definition',
+      nargs='?',
+      default=CANONICAL_PROJECT_STRUCT_FILE,
+      type=str,
+      help=(
+        f'Path to the YAML configuration file (default: {CANONICAL_PROJECT_STRUCT_FILE}; '
+        f'falls back to {LEGACY_PROJECT_STRUCT_FILE} for compatibility)'
+      ),
+    )
     structure_arg.completer = structures_completer
     parser.add_argument('base_path', nargs='?', default='.', type=str, help='Base path where the structure will be created (default: current directory)')
     parser.add_argument(
@@ -246,6 +260,9 @@ def _validate_loaded_config(self, config):
     return config
 
   def execute(self, args):
+    args.structure_definition = resolve_project_struct_file(
+      explicit_path=getattr(args, 'structure_definition', None),
+    )
     try:
       args.structures_path, args.structure_definition = resolve_structures_path(
         args.structures_path,
diff --git a/structkit/commands/init.py b/structkit/commands/init.py
index 4cd89ff..73c7b31 100644
--- a/structkit/commands/init.py
+++ b/structkit/commands/init.py
@@ -1,6 +1,10 @@
 from structkit.commands import Command
 import os
 import textwrap
+from structkit.project_file import (
+    CANONICAL_PROJECT_STRUCT_FILE,
+    LEGACY_PROJECT_STRUCT_FILE,
+)
 
 BASIC_STRUCTKIT_YAML = textwrap.dedent(
     """
@@ -17,7 +21,7 @@
       - README.md: |
           # Project
 
-          Initialized with struct.
+          Initialized with structkit.
 
     folders:
       - ./:
@@ -30,24 +34,33 @@
 class InitCommand(Command):
   def __init__(self, parser):
     super().__init__(parser)
-    parser.description = "Initialize a basic .struct.yaml in the target directory"
+    parser.description = f"Initialize a basic {CANONICAL_PROJECT_STRUCT_FILE} in the target directory"
     parser.add_argument('path', nargs='?', default='.', help='Directory to initialize (default: current directory)')
     parser.set_defaults(func=self.execute)
 
   def execute(self, args):
     base_path = os.path.abspath(args.path or '.')
-    target = os.path.join(base_path, '.struct.yaml')
+    target = os.path.join(base_path, CANONICAL_PROJECT_STRUCT_FILE)
+    legacy = os.path.join(base_path, LEGACY_PROJECT_STRUCT_FILE)
 
     os.makedirs(base_path, exist_ok=True)
 
-    # If file exists, do not overwrite without explicit confirmation behavior (keep simple: skip)
+    # If either canonical or legacy file exists, do not overwrite.
     if os.path.exists(target):
-      self.logger.info(f".struct.yaml already exists at {target}, skipping creation")
-      print(f"⚠️  .struct.yaml already exists at: {target}")
+      self.logger.info(f"{CANONICAL_PROJECT_STRUCT_FILE} already exists at {target}, skipping creation")
+      print(f"⚠️  {CANONICAL_PROJECT_STRUCT_FILE} already exists at: {target}")
+      return
+
+    if os.path.exists(legacy):
+      self.logger.info(
+        f"{LEGACY_PROJECT_STRUCT_FILE} already exists at {legacy}, skipping creation"
+      )
+      print(f"⚠️  {LEGACY_PROJECT_STRUCT_FILE} already exists at: {legacy}")
+      print(f"   Consider renaming it to {CANONICAL_PROJECT_STRUCT_FILE}.")
       return
 
     with open(target, 'w') as f:
       f.write(BASIC_STRUCTKIT_YAML)
 
-    print("✅ Created .struct.yaml")
+    print(f"✅ Created {CANONICAL_PROJECT_STRUCT_FILE}")
     print(f" - {target}")
diff --git a/structkit/config.py b/structkit/config.py
index dbe38b9..a41afe4 100644
--- a/structkit/config.py
+++ b/structkit/config.py
@@ -3,7 +3,7 @@
 Supports loading and merging configuration from multiple sources:
 1. Built-in defaults
 2. User config (~/.config/struct/config.yaml)
-3. Project config (.struct.yaml or --config-file)
+3. Project config (.structkit.yaml, legacy .struct.yaml, or --config-file)
 4. CLI arguments
 
 Priority order: CLI args > Project config > User config > Built-in defaults
diff --git a/structkit/contribs/README.md b/structkit/contribs/README.md
index 19e984c..de7aa67 100644
--- a/structkit/contribs/README.md
+++ b/structkit/contribs/README.md
@@ -194,8 +194,8 @@ The `contribs` folder contains various sub-structs that can be used to generate
 
 #### `github/prompts/struct`
 
-- **Description**: Provides a prompt for creating a new .struct.yaml file and workflow to run struct.
-- **When to Use**: Use this sub-structkit when you need to create a new .struct.yaml file and workflow to run struct.
+- **Description**: Provides a prompt for creating a new .structkit.yaml file and workflow to run struct.
+- **When to Use**: Use this sub-structkit when you need to create a new .structkit.yaml file and workflow to run struct.
 
 ### Project
 
diff --git a/structkit/contribs/github/prompts/struct.yaml b/structkit/contribs/github/prompts/struct.yaml
index 28818bc..fb11b91 100644
--- a/structkit/contribs/github/prompts/struct.yaml
+++ b/structkit/contribs/github/prompts/struct.yaml
@@ -1,6 +1,6 @@
 description: >
   Creates a GitHub Copilot prompt that configures an AI assistant for generating
-  valid .struct.yaml files for the StructKit tool, with schema references and usage examples.
+  valid .structkit.yaml files for the StructKit tool, with schema references and usage examples.
 
 files:
   - .github/prompts/struct.prompt.md:
@@ -9,9 +9,9 @@ files:
 
         ## Role
 
-        You are an expert assistant that generates valid `.struct.yaml` files for the [StructKit tool](https://github.com/httpdss/struct), which automates project structure generation from YAML configuration.
+        You are an expert assistant that generates valid `.structkit.yaml` files for the [StructKit tool](https://github.com/httpdss/struct), which automates project structure generation from YAML configuration.
 
-        ## Defining the `.struct.yaml` file
+        ## Defining the `.structkit.yaml` file
 
         this file has 3 main keys: `structures`, `folders`, and `variables`.
 
diff --git a/structkit/contribs/github/workflows/run-struct.yaml b/structkit/contribs/github/workflows/run-struct.yaml
index 798b32d..90a5eac 100644
--- a/structkit/contribs/github/workflows/run-struct.yaml
+++ b/structkit/contribs/github/workflows/run-struct.yaml
@@ -1,6 +1,6 @@
 description: >
   Creates a GitHub Actions workflow (run-struct.yaml) that can be manually triggered
-  via workflow_dispatch to run struct file generation, plus a starter .struct.yaml file.
+  via workflow_dispatch to run struct file generation, plus a starter .structkit.yaml file.
 
 files:
   - .github/workflows/run-struct.yaml:
@@ -15,11 +15,11 @@ files:
           generate:
             uses: httpdss/structkit/.github/workflows/struct-generate.yaml@main
             with:
-              struct_file: 'file://.struct.yaml'
+              struct_file: 'file://.structkit.yaml'
               output_dir: '.'
             secrets:
               token: {{@ github_token @}}
-  - .struct.yaml:
+  - .structkit.yaml:
       skip_if_exists: true
       content: |
         files:
diff --git a/structkit/main.py b/structkit/main.py
index 12ca15d..99a9e69 100644
--- a/structkit/main.py
+++ b/structkit/main.py
@@ -141,9 +141,9 @@ def get_parser():
     SourcesCommand(subparsers.add_parser('sources', help='Manage named custom structure sources'))
     ConfigCommand(subparsers.add_parser('config', help='Display and manage structkit configuration'))
 
-    # init to create a basic .struct.yaml
+    # init to create a basic .structkit.yaml
     from structkit.commands.init import InitCommand
-    InitCommand(subparsers.add_parser('init', help='Initialize a basic .struct.yaml in the target directory'))
+    InitCommand(subparsers.add_parser('init', help='Initialize a basic .structkit.yaml in the target directory'))
 
     # completion manager
     from structkit.commands.completion import CompletionCommand
diff --git a/structkit/project_file.py b/structkit/project_file.py
new file mode 100644
index 0000000..cde8b1b
--- /dev/null
+++ b/structkit/project_file.py
@@ -0,0 +1,113 @@
+"""Canonical and legacy project structure filenames.
+
+The product was originally named STRUCT, so repositories commonly commit
+``.struct.yaml``. The canonical name is now ``.structkit.yaml``. Commands that
+default to the project structure file prefer the canonical name and fall back
+to the legacy name when it is the only one present.
+"""
+
+import logging
+import os
+from typing import Optional, Tuple
+
+logger = logging.getLogger(__name__)
+
+CANONICAL_PROJECT_STRUCT_FILE = ".structkit.yaml"
+LEGACY_PROJECT_STRUCT_FILE = ".struct.yaml"
+PROJECT_STRUCT_FILES = (
+    CANONICAL_PROJECT_STRUCT_FILE,
+    LEGACY_PROJECT_STRUCT_FILE,
+)
+
+
+def strip_file_scheme(path: str) -> Tuple[str, bool]:
+    """Return (local_path, had_file_scheme) for a structure path."""
+    if path.startswith("file://"):
+        return path[7:], True
+    return path, False
+
+
+def is_default_project_struct_path(path: Optional[str]) -> bool:
+    """Return True when path is omitted or names a default project file."""
+    if not path:
+        return True
+    local_path, _ = strip_file_scheme(path)
+    return os.path.basename(local_path) in PROJECT_STRUCT_FILES
+
+
+def find_existing_project_struct_file(directory: str = ".") -> Optional[str]:
+    """Return the existing default project file in directory, if any.
+
+    Prefers ``.structkit.yaml`` over the legacy ``.struct.yaml``.
+    """
+    canonical = os.path.join(directory, CANONICAL_PROJECT_STRUCT_FILE)
+    if os.path.isfile(canonical):
+        return canonical
+
+    legacy = os.path.join(directory, LEGACY_PROJECT_STRUCT_FILE)
+    if os.path.isfile(legacy):
+        return legacy
+
+    return None
+
+
+def resolve_project_struct_file(
+    explicit_path: Optional[str] = None,
+    directory: str = ".",
+) -> str:
+    """Resolve which project structure file a command should use.
+
+    Non-default paths (named structures, custom YAML files) are returned
+    unchanged. Default names prefer ``.structkit.yaml`` and fall back to
+    ``.struct.yaml`` when the canonical file is missing.
+
+    If neither default file exists, the canonical name is returned so error
+    messages mention ``.structkit.yaml``.
+    """
+    if explicit_path and not is_default_project_struct_path(explicit_path):
+        return explicit_path
+
+    file_scheme = False
+    search_dir = directory
+    if explicit_path:
+        local_path, file_scheme = strip_file_scheme(explicit_path)
+        parent = os.path.dirname(local_path)
+        if parent:
+            search_dir = parent
+            existing_path = local_path
+        else:
+            existing_path = os.path.join(directory, os.path.basename(local_path))
+        if os.path.isfile(existing_path):
+            return explicit_path
+
+    canonical = os.path.normpath(os.path.join(search_dir, CANONICAL_PROJECT_STRUCT_FILE))
+    legacy = os.path.normpath(os.path.join(search_dir, LEGACY_PROJECT_STRUCT_FILE))
+
+    if os.path.isfile(canonical):
+        if os.path.isfile(legacy):
+            logger.info(
+                "Both %s and %s exist; using %s. Rename or remove %s to avoid ambiguity.",
+                CANONICAL_PROJECT_STRUCT_FILE,
+                LEGACY_PROJECT_STRUCT_FILE,
+                CANONICAL_PROJECT_STRUCT_FILE,
+                LEGACY_PROJECT_STRUCT_FILE,
+            )
+        chosen = canonical
+    elif os.path.isfile(legacy):
+        logger.info(
+            "Using legacy %s; prefer renaming it to %s.",
+            LEGACY_PROJECT_STRUCT_FILE,
+            CANONICAL_PROJECT_STRUCT_FILE,
+        )
+        chosen = legacy
+    else:
+        chosen = canonical
+
+    if file_scheme:
+        return f"file://{chosen}"
+    if explicit_path and os.path.dirname(explicit_path) in ("", "."):
+        # Keep a bare filename when the caller passed one (argparse default).
+        return os.path.basename(chosen)
+    if explicit_path is None and search_dir in ("", "."):
+        return os.path.basename(chosen)
+    return chosen
diff --git a/tests/test_init_command.py b/tests/test_init_command.py
index e7a88ad..e40ce5c 100644
--- a/tests/test_init_command.py
+++ b/tests/test_init_command.py
@@ -1,8 +1,7 @@
 import argparse
-import os
 from unittest.mock import patch
 
-from structkit.commands.init import InitCommand, BASIC_STRUCTKIT_YAML
+from structkit.commands.init import InitCommand
 
 
 def test_init_creates_struct_yaml(tmp_path):
@@ -12,10 +11,10 @@ def test_init_creates_struct_yaml(tmp_path):
     target_dir = tmp_path / "proj"
     args = parser.parse_args([str(target_dir)])
 
-    with patch('builtins.print') as mock_print:
+    with patch('builtins.print'):
         cmd.execute(args)
 
-    struct_file = target_dir / '.struct.yaml'
+    struct_file = target_dir / '.structkit.yaml'
     assert struct_file.exists()
 
     content = struct_file.read_text()
@@ -34,7 +33,7 @@ def test_init_skips_if_exists(tmp_path):
 
     target_dir = tmp_path / "proj"
     target_dir.mkdir(parents=True)
-    existing = target_dir / '.struct.yaml'
+    existing = target_dir / '.structkit.yaml'
     existing.write_text('files: []\n')
 
     args = parser.parse_args([str(target_dir)])
@@ -45,4 +44,4 @@ def test_init_skips_if_exists(tmp_path):
         assert existing.read_text() == 'files: []\n'
         # Should print a message about skipping
         printed = "\n".join(c.args[0] for c in mock_print.call_args_list)
-        assert '.struct.yaml already exists' in printed
+        assert '.structkit.yaml already exists' in printed
diff --git a/tests/test_project_file.py b/tests/test_project_file.py
new file mode 100644
index 0000000..55928e7
--- /dev/null
+++ b/tests/test_project_file.py
@@ -0,0 +1,166 @@
+import argparse
+
+from structkit.commands.generate import GenerateCommand
+from structkit.commands.init import InitCommand
+from structkit.project_file import (
+    CANONICAL_PROJECT_STRUCT_FILE,
+    LEGACY_PROJECT_STRUCT_FILE,
+    find_existing_project_struct_file,
+    is_default_project_struct_path,
+    resolve_project_struct_file,
+    strip_file_scheme,
+)
+
+
+def test_strip_file_scheme():
+    assert strip_file_scheme("file://.structkit.yaml") == (".structkit.yaml", True)
+    assert strip_file_scheme(".struct.yaml") == (".struct.yaml", False)
+
+
+def test_is_default_project_struct_path():
+    assert is_default_project_struct_path(None) is True
+    assert is_default_project_struct_path("") is True
+    assert is_default_project_struct_path(".structkit.yaml") is True
+    assert is_default_project_struct_path(".struct.yaml") is True
+    assert is_default_project_struct_path("file://.struct.yaml") is True
+    assert is_default_project_struct_path("examples/app/.structkit.yaml") is True
+    assert is_default_project_struct_path("project/python") is False
+    assert is_default_project_struct_path("my-config.yaml") is False
+
+
+def test_find_existing_prefers_canonical(tmp_path):
+    (tmp_path / CANONICAL_PROJECT_STRUCT_FILE).write_text("files: []\n")
+    (tmp_path / LEGACY_PROJECT_STRUCT_FILE).write_text("files: []\n")
+
+    found = find_existing_project_struct_file(str(tmp_path))
+
+    assert found.endswith(CANONICAL_PROJECT_STRUCT_FILE)
+
+
+def test_find_existing_falls_back_to_legacy(tmp_path):
+    (tmp_path / LEGACY_PROJECT_STRUCT_FILE).write_text("files: []\n")
+
+    found = find_existing_project_struct_file(str(tmp_path))
+
+    assert found.endswith(LEGACY_PROJECT_STRUCT_FILE)
+
+
+def test_find_existing_returns_none_when_missing(tmp_path):
+    assert find_existing_project_struct_file(str(tmp_path)) is None
+
+
+def test_resolve_leaves_named_structures_unchanged():
+    assert resolve_project_struct_file("project/python") == "project/python"
+    assert resolve_project_struct_file("file://custom.yaml") == "file://custom.yaml"
+
+
+def test_resolve_prefers_canonical_when_both_exist(tmp_path):
+    (tmp_path / CANONICAL_PROJECT_STRUCT_FILE).write_text("canonical: true\n")
+    (tmp_path / LEGACY_PROJECT_STRUCT_FILE).write_text("legacy: true\n")
+
+    resolved = resolve_project_struct_file(directory=str(tmp_path))
+
+    assert resolved.endswith(CANONICAL_PROJECT_STRUCT_FILE)
+
+
+def test_resolve_falls_back_to_legacy_default_name(tmp_path):
+    (tmp_path / LEGACY_PROJECT_STRUCT_FILE).write_text("legacy: true\n")
+
+    resolved = resolve_project_struct_file(
+        explicit_path=CANONICAL_PROJECT_STRUCT_FILE,
+        directory=str(tmp_path),
+    )
+
+    assert resolved.endswith(LEGACY_PROJECT_STRUCT_FILE)
+
+
+def test_resolve_keeps_explicit_legacy_file_when_it_exists(tmp_path):
+    (tmp_path / CANONICAL_PROJECT_STRUCT_FILE).write_text("canonical: true\n")
+    (tmp_path / LEGACY_PROJECT_STRUCT_FILE).write_text("legacy: true\n")
+    explicit = str(tmp_path / LEGACY_PROJECT_STRUCT_FILE)
+
+    resolved = resolve_project_struct_file(explicit_path=explicit, directory=str(tmp_path))
+
+    assert resolved == explicit
+
+
+def test_resolve_rewrites_missing_legacy_path_to_canonical(tmp_path):
+    (tmp_path / CANONICAL_PROJECT_STRUCT_FILE).write_text("canonical: true\n")
+    explicit = str(tmp_path / LEGACY_PROJECT_STRUCT_FILE)
+
+    resolved = resolve_project_struct_file(explicit_path=explicit, directory=str(tmp_path))
+
+    assert resolved.endswith(CANONICAL_PROJECT_STRUCT_FILE)
+
+
+def test_resolve_preserves_file_scheme_on_fallback(tmp_path):
+    (tmp_path / LEGACY_PROJECT_STRUCT_FILE).write_text("legacy: true\n")
+    explicit = f"file://{tmp_path / CANONICAL_PROJECT_STRUCT_FILE}"
+
+    resolved = resolve_project_struct_file(explicit_path=explicit, directory=str(tmp_path))
+
+    assert resolved.startswith("file://")
+    assert resolved.endswith(LEGACY_PROJECT_STRUCT_FILE)
+
+
+def test_resolve_returns_canonical_when_neither_exists(tmp_path):
+    resolved = resolve_project_struct_file(directory=str(tmp_path))
+    assert resolved.endswith(CANONICAL_PROJECT_STRUCT_FILE)
+
+
+def test_generate_uses_legacy_struct_yaml_when_canonical_missing(tmp_path, monkeypatch):
+    monkeypatch.chdir(tmp_path)
+    (tmp_path / LEGACY_PROJECT_STRUCT_FILE).write_text(
+        "files:\n  - hello.txt:\n      content: from-legacy\n"
+    )
+    out_dir = tmp_path / "out"
+    parser = argparse.ArgumentParser()
+    command = GenerateCommand(parser)
+    args = parser.parse_args(["--non-interactive", CANONICAL_PROJECT_STRUCT_FILE, str(out_dir)])
+
+    command.execute(args)
+
+    assert (out_dir / "hello.txt").read_text().strip() == "from-legacy"
+
+
+def test_generate_prefers_structkit_yaml_when_both_exist(tmp_path, monkeypatch):
+    monkeypatch.chdir(tmp_path)
+    (tmp_path / LEGACY_PROJECT_STRUCT_FILE).write_text(
+        "files:\n  - hello.txt:\n      content: from-legacy\n"
+    )
+    (tmp_path / CANONICAL_PROJECT_STRUCT_FILE).write_text(
+        "files:\n  - hello.txt:\n      content: from-canonical\n"
+    )
+    out_dir = tmp_path / "out"
+    parser = argparse.ArgumentParser()
+    command = GenerateCommand(parser)
+    args = parser.parse_args(["--non-interactive", CANONICAL_PROJECT_STRUCT_FILE, str(out_dir)])
+
+    command.execute(args)
+
+    assert (out_dir / "hello.txt").read_text().strip() == "from-canonical"
+
+
+def test_init_skips_legacy_struct_yaml(tmp_path):
+    parser = argparse.ArgumentParser()
+    cmd = InitCommand(parser)
+    target_dir = tmp_path / "proj"
+    target_dir.mkdir()
+    existing = target_dir / LEGACY_PROJECT_STRUCT_FILE
+    existing.write_text("files: []\n")
+
+    args = parser.parse_args([str(target_dir)])
+    printed = []
+
+    def capture(message):
+        printed.append(message)
+
+    from unittest.mock import patch
+    with patch("builtins.print", side_effect=capture):
+        cmd.execute(args)
+
+    assert existing.read_text() == "files: []\n"
+    assert not (target_dir / CANONICAL_PROJECT_STRUCT_FILE).exists()
+    output = "\n".join(printed)
+    assert LEGACY_PROJECT_STRUCT_FILE in output
+    assert CANONICAL_PROJECT_STRUCT_FILE in output
diff --git a/tests/test_sources_command.py b/tests/test_sources_command.py
index 7e6688e..9f0b7dd 100644
--- a/tests/test_sources_command.py
+++ b/tests/test_sources_command.py
@@ -208,7 +208,7 @@ def test_file_local_sources_resolve_nested_structs(monkeypatch, tmp_path):
     )
     (local_source / "child.yaml").write_text("files:\n  - child.txt:\n      content: local\n")
 
-    root = tmp_path / ".struct.yaml"
+    root = tmp_path / ".structkit.yaml"
     root.write_text(
         "sources:\n"
         f"  platform:\n"
@@ -239,7 +239,7 @@ def test_nested_source_redefinition_is_rejected(tmp_path):
         "files: []\n"
     )
 
-    root = tmp_path / ".struct.yaml"
+    root = tmp_path / ".structkit.yaml"
     root.write_text(
         "sources:\n"
         f"  platform:\n"