diff --git a/.github/workflows/cli-ci.yml b/.github/workflows/cli-ci.yml
new file mode 100644
index 0000000..e729089
--- /dev/null
+++ b/.github/workflows/cli-ci.yml
@@ -0,0 +1,38 @@
+name: CLI CI
+
+on:
+  push:
+    paths:
+      - 'cli/**'
+      - '.github/workflows/cli-ci.yml'
+  pull_request:
+    paths:
+      - 'cli/**'
+      - '.github/workflows/cli-ci.yml'
+
+jobs:
+  build-and-test:
+    name: Build and test
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: cli
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version-file: cli/go.mod
+          cache-dependency-path: cli/go.sum
+
+      - name: go build
+        run: go build ./...
+
+      - name: go vet
+        run: go vet ./...
+
+      - name: go test
+        run: go test ./...
diff --git a/.gitignore b/.gitignore
index 63e36ff..8cf6aa8 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,6 @@
 **/__pycache__/
 **/.venv/
+
+# Go CLI
+cli/dist/
+cli/osi
diff --git a/cli/.goreleaser.yaml b/cli/.goreleaser.yaml
new file mode 100644
index 0000000..3a0a17b
--- /dev/null
+++ b/cli/.goreleaser.yaml
@@ -0,0 +1,48 @@
+version: 2
+
+project_name: ossie
+
+before:
+  hooks:
+    - go mod tidy
+
+builds:
+  - id: ossie
+    main: .
+    binary: ossie
+    goos:
+      - linux
+      - darwin
+      - windows
+    goarch:
+      - amd64
+      - arm64
+    ignore:
+      - goos: windows
+        goarch: arm64
+    env:
+      - CGO_ENABLED=0
+    ldflags:
+      - -s -w
+      - -X main.version={{.Version}}
+      - -X main.commit={{.Commit}}
+      - -X main.date={{.Date}}
+
+archives:
+  - id: ossie
+    format: tar.gz
+    format_overrides:
+      - goos: windows
+        format: zip
+    name_template: "{{ .ProjectName }}_{{ .Version }}_{{ .Os }}_{{ .Arch }}"
+
+checksum:
+  name_template: "checksums.txt"
+
+changelog:
+  sort: asc
+  filters:
+    exclude:
+      - "^docs:"
+      - "^test:"
+      - "^chore:"
diff --git a/cli/.tool-versions b/cli/.tool-versions
new file mode 100644
index 0000000..05a23a6
--- /dev/null
+++ b/cli/.tool-versions
@@ -0,0 +1 @@
+golang 1.26.2
diff --git a/cli/Makefile b/cli/Makefile
new file mode 100644
index 0000000..9ecbcb7
--- /dev/null
+++ b/cli/Makefile
@@ -0,0 +1,19 @@
+BINARY_NAME := ossie
+BUILD_DIR   := dist
+
+.PHONY: build test lint release-dry-run clean
+
+build:
+	go build -o $(BUILD_DIR)/$(BINARY_NAME) .
+
+test:
+	go test ./...
+
+lint:
+	go vet ./...
+
+release-dry-run:
+	goreleaser release --snapshot --clean --config .goreleaser.yaml
+
+clean:
+	rm -rf $(BUILD_DIR)
diff --git a/cli/cmd/convert.go b/cli/cmd/convert.go
new file mode 100644
index 0000000..92722ee
--- /dev/null
+++ b/cli/cmd/convert.go
@@ -0,0 +1,39 @@
+package cmd
+
+import (
+	"fmt"
+
+	"github.com/spf13/cobra"
+)
+
+var convertCmd = &cobra.Command{
+	Use:   "convert --from <platform> --input <path> | --to <platform> --input <path>",
+	Short: "Convert a semantic model between OSSIE and a platform format",
+	RunE:  runConvert,
+}
+
+func init() {
+	convertCmd.Flags().String("from", "", "Source platform — converts platform → OSSIE")
+	convertCmd.Flags().String("to", "", "Target platform — converts OSSIE → platform")
+	convertCmd.Flags().StringP("input", "i", "", "Input file or directory path (required)")
+	convertCmd.Flags().StringP("output", "o", "", "Output directory path (default: ./ossie-output/<plugin>/<direction>)")
+	convertCmd.Flags().String("plugin", "", "Path to plugin directory (bypasses name-based discovery)")
+	convertCmd.Flags().Int("timeout", 60, "Plugin invocation timeout in seconds")
+	convertCmd.Flags().String("max-input-size", "100MB", "Maximum total input size (e.g. 500MB)")
+
+	_ = convertCmd.MarkFlagRequired("input")
+	convertCmd.MarkFlagsMutuallyExclusive("from", "to")
+}
+
+func runConvert(cmd *cobra.Command, args []string) error {
+	from, _ := cmd.Flags().GetString("from")
+	to, _ := cmd.Flags().GetString("to")
+
+	// MarkFlagsMutuallyExclusive handles the both-set case; handle neither here.
+	if from == "" && to == "" {
+		return fmt.Errorf("exactly one of --from or --to must be specified")
+	}
+
+	fmt.Fprintln(cmd.OutOrStdout(), "not yet implemented")
+	return nil
+}
diff --git a/cli/cmd/plugin/install.go b/cli/cmd/plugin/install.go
new file mode 100644
index 0000000..aabde2d
--- /dev/null
+++ b/cli/cmd/plugin/install.go
@@ -0,0 +1,22 @@
+package plugin
+
+import (
+	"fmt"
+
+	"github.com/spf13/cobra"
+)
+
+var installCmd = &cobra.Command{
+	Use:   "install [name[@version] | url]",
+	Short: "Install a plugin from the registry or a URL",
+	RunE:  runPluginInstall,
+}
+
+func init() {
+	installCmd.Flags().Bool("all", false, "Install the latest version of all registry plugins")
+}
+
+func runPluginInstall(cmd *cobra.Command, args []string) error {
+	fmt.Fprintln(cmd.OutOrStdout(), "not yet implemented")
+	return nil
+}
diff --git a/cli/cmd/plugin/list.go b/cli/cmd/plugin/list.go
new file mode 100644
index 0000000..f69e8bb
--- /dev/null
+++ b/cli/cmd/plugin/list.go
@@ -0,0 +1,18 @@
+package plugin
+
+import (
+	"fmt"
+
+	"github.com/spf13/cobra"
+)
+
+var listCmd = &cobra.Command{
+	Use:   "list",
+	Short: "List installed and available plugins",
+	RunE:  runPluginList,
+}
+
+func runPluginList(cmd *cobra.Command, args []string) error {
+	fmt.Fprintln(cmd.OutOrStdout(), "not yet implemented")
+	return nil
+}
diff --git a/cli/cmd/plugin/plugin.go b/cli/cmd/plugin/plugin.go
new file mode 100644
index 0000000..d996f13
--- /dev/null
+++ b/cli/cmd/plugin/plugin.go
@@ -0,0 +1,16 @@
+package plugin
+
+import "github.com/spf13/cobra"
+
+// Cmd is the parent "ossie plugin" command. It is exported so cmd/root.go can
+// register it. Invoking it bare prints help.
+var Cmd = &cobra.Command{
+	Use:   "plugin",
+	Short: "Manage OSSIE plugins",
+}
+
+func init() {
+	Cmd.AddCommand(listCmd)
+	Cmd.AddCommand(installCmd)
+	Cmd.AddCommand(removeCmd)
+}
diff --git a/cli/cmd/plugin/remove.go b/cli/cmd/plugin/remove.go
new file mode 100644
index 0000000..1b88669
--- /dev/null
+++ b/cli/cmd/plugin/remove.go
@@ -0,0 +1,19 @@
+package plugin
+
+import (
+	"fmt"
+
+	"github.com/spf13/cobra"
+)
+
+var removeCmd = &cobra.Command{
+	Use:   "remove <name>",
+	Short: "Remove an installed plugin",
+	Args:  cobra.ExactArgs(1),
+	RunE:  runPluginRemove,
+}
+
+func runPluginRemove(cmd *cobra.Command, args []string) error {
+	fmt.Fprintln(cmd.OutOrStdout(), "not yet implemented")
+	return nil
+}
diff --git a/cli/cmd/root.go b/cli/cmd/root.go
new file mode 100644
index 0000000..772d87b
--- /dev/null
+++ b/cli/cmd/root.go
@@ -0,0 +1,38 @@
+package cmd
+
+import (
+	"github.com/open-semantic-interchange/ossie/cli/cmd/plugin"
+	"github.com/open-semantic-interchange/ossie/cli/internal/ossiedir"
+	"github.com/spf13/cobra"
+)
+
+var rootCmd = &cobra.Command{
+	Use:   "ossie",
+	Short: "Open Semantic Interchange CLI",
+	Long:  `ossie is the command-line tool for the Open Semantic Interchange (OSSIE) project.`,
+	// NOTE: Cobra does NOT automatically chain PersistentPreRunE from parent to
+	// child. If any subcommand defines its own PersistentPreRunE or PreRunE, this
+	// function will not run for that subcommand. Future subcommands that define
+	// their own must call ossiedir.EnsurePluginDir() explicitly.
+	PersistentPreRunE: func(cmd *cobra.Command, args []string) error {
+		return ossiedir.EnsurePluginDir()
+	},
+}
+
+// Execute runs the root command. Called by main.
+func Execute() error {
+	return rootCmd.Execute()
+}
+
+// SetVersion sets the version string reported by `ossie --version`.
+func SetVersion(v string) {
+	rootCmd.Version = v
+}
+
+func init() {
+	rootCmd.PersistentFlags().BoolP("verbose", "v", false, "Enable verbose output (shows plugin stderr)")
+
+	rootCmd.AddCommand(convertCmd)
+	rootCmd.AddCommand(validateCmd)
+	rootCmd.AddCommand(plugin.Cmd)
+}
diff --git a/cli/cmd/validate.go b/cli/cmd/validate.go
new file mode 100644
index 0000000..b11d00a
--- /dev/null
+++ b/cli/cmd/validate.go
@@ -0,0 +1,24 @@
+package cmd
+
+import (
+	"fmt"
+
+	"github.com/spf13/cobra"
+)
+
+var validateCmd = &cobra.Command{
+	Use:   "validate [flags] <path> [<path>...]",
+	Short: "Validate one or more OSSIE YAML or JSON files",
+	Args:  cobra.MinimumNArgs(1),
+	RunE:  runValidate,
+}
+
+func init() {
+	validateCmd.Flags().Bool("strict", false, "Promote warnings to errors")
+	validateCmd.Flags().String("output", "text", "Output format: text or json")
+}
+
+func runValidate(cmd *cobra.Command, args []string) error {
+	fmt.Fprintln(cmd.OutOrStdout(), "not yet implemented")
+	return nil
+}
diff --git a/cli/go.mod b/cli/go.mod
new file mode 100644
index 0000000..a828425
--- /dev/null
+++ b/cli/go.mod
@@ -0,0 +1,10 @@
+module github.com/open-semantic-interchange/ossie/cli
+
+go 1.22
+
+require github.com/spf13/cobra v1.10.2
+
+require (
+	github.com/inconshreveable/mousetrap v1.1.0 // indirect
+	github.com/spf13/pflag v1.0.9 // indirect
+)
diff --git a/cli/go.sum b/cli/go.sum
new file mode 100644
index 0000000..a6ee3e0
--- /dev/null
+++ b/cli/go.sum
@@ -0,0 +1,10 @@
+github.com/cpuguy83/go-md2man/v2 v2.0.6/go.mod h1:oOW0eioCTA6cOiMLiUPZOpcVxMig6NIQQ7OS05n1F4g=
+github.com/inconshreveable/mousetrap v1.1.0 h1:wN+x4NVGpMsO7ErUn/mUI3vEoE6Jt13X2s0bqwp9tc8=
+github.com/inconshreveable/mousetrap v1.1.0/go.mod h1:vpF70FUmC8bwa3OWnCshd2FqLfsEA9PFc4w1p2J65bw=
+github.com/russross/blackfriday/v2 v2.1.0/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=
+github.com/spf13/cobra v1.10.2 h1:DMTTonx5m65Ic0GOoRY2c16WCbHxOOw6xxezuLaBpcU=
+github.com/spf13/cobra v1.10.2/go.mod h1:7C1pvHqHw5A4vrJfjNwvOdzYu0Gml16OCs2GRiTUUS4=
+github.com/spf13/pflag v1.0.9 h1:9exaQaMOCwffKiiiYk6/BndUBv+iRViNW+4lEMi0PvY=
+github.com/spf13/pflag v1.0.9/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
+go.yaml.in/yaml/v3 v3.0.4/go.mod h1:DhzuOOF2ATzADvBadXxruRBLzYTpT36CKvDb3+aBEFg=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
diff --git a/cli/internal/ossiedir/osidir.go b/cli/internal/ossiedir/osidir.go
new file mode 100644
index 0000000..9396041
--- /dev/null
+++ b/cli/internal/ossiedir/osidir.go
@@ -0,0 +1,40 @@
+package ossiedir
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+)
+
+const (
+	defaultOSIDir = ".ossie"
+	pluginsSubdir = "plugins"
+	envVar        = "OSSIE_PLUGIN_DIR"
+)
+
+// PluginDir returns the resolved plugin directory path.
+// It respects $OSSIE_PLUGIN_DIR if set, otherwise defaults to ~/.ossie/plugins/.
+func PluginDir() (string, error) {
+	if override := os.Getenv(envVar); override != "" {
+		return override, nil
+	}
+	// Use os.UserHomeDir rather than $HOME for Windows portability.
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return "", fmt.Errorf("could not determine home directory: %w", err)
+	}
+	return filepath.Join(home, defaultOSIDir, pluginsSubdir), nil
+}
+
+// EnsurePluginDir ensures the plugin directory exists, creating it if needed.
+// It is safe to call multiple times — os.MkdirAll is idempotent.
+func EnsurePluginDir() error {
+	dir, err := PluginDir()
+	if err != nil {
+		return err
+	}
+	if err := os.MkdirAll(dir, 0755); err != nil {
+		return fmt.Errorf("could not create plugin directory %s: %w", dir, err)
+	}
+	return nil
+}
diff --git a/cli/internal/ossiedir/osidir_test.go b/cli/internal/ossiedir/osidir_test.go
new file mode 100644
index 0000000..0fe341c
--- /dev/null
+++ b/cli/internal/ossiedir/osidir_test.go
@@ -0,0 +1,65 @@
+package ossiedir
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestPluginDir_envOverride(t *testing.T) {
+	want := "/custom/plugin/dir"
+	t.Setenv(envVar, want)
+
+	got, err := PluginDir()
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if got != want {
+		t.Errorf("got %q, want %q", got, want)
+	}
+}
+
+func TestPluginDir_default(t *testing.T) {
+	t.Setenv(envVar, "")
+
+	home, err := os.UserHomeDir()
+	if err != nil {
+		t.Fatalf("could not determine home dir: %v", err)
+	}
+	want := filepath.Join(home, defaultOSIDir, pluginsSubdir)
+
+	got, err := PluginDir()
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if got != want {
+		t.Errorf("got %q, want %q", got, want)
+	}
+}
+
+func TestEnsurePluginDir_createsDirectory(t *testing.T) {
+	tmp := t.TempDir()
+	target := filepath.Join(tmp, "plugins")
+	t.Setenv(envVar, target)
+
+	if err := EnsurePluginDir(); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	if _, err := os.Stat(target); os.IsNotExist(err) {
+		t.Errorf("expected directory %q to exist, but it does not", target)
+	}
+}
+
+func TestEnsurePluginDir_idempotent(t *testing.T) {
+	tmp := t.TempDir()
+	target := filepath.Join(tmp, "plugins")
+	t.Setenv(envVar, target)
+
+	if err := EnsurePluginDir(); err != nil {
+		t.Fatalf("first call failed: %v", err)
+	}
+	if err := EnsurePluginDir(); err != nil {
+		t.Fatalf("second call failed: %v", err)
+	}
+}
diff --git a/cli/main.go b/cli/main.go
new file mode 100644
index 0000000..9d2a202
--- /dev/null
+++ b/cli/main.go
@@ -0,0 +1,21 @@
+package main
+
+import (
+	"os"
+
+	"github.com/open-semantic-interchange/ossie/cli/cmd"
+)
+
+// version, commit, and date are set at build time by GoReleaser via ldflags.
+var (
+	version = "dev"
+	commit  = "none"
+	date    = "unknown"
+)
+
+func main() {
+	cmd.SetVersion(version)
+	if err := cmd.Execute(); err != nil {
+		os.Exit(1)
+	}
+}