diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 4d40518..e0d9b79 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -25,7 +25,7 @@ jobs:
       - run: uv run ruff format --check .
       - run: uv run ruff check .
       - run: uv run mypy
-      - run: uv run pytest
+      - run: uv run pytest -n auto
 
   workflows:
     runs-on: ubuntu-24.04
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index f4b6d93..e19ba9d 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -19,7 +19,7 @@ repos:
         types: [python]
       - id: pytest
         name: pytest
-        entry: uv run pytest
+        entry: uv run pytest -n auto
         language: system
         pass_filenames: false
         always_run: true
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 0629d50..d1fe51a 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -73,7 +73,7 @@ Run each with `uv run python tools/<script>`.
 CI runs the same checks:
 
 ```sh
-uv run ruff format . && uv run ruff check . && uv run mypy && uv run pytest
+uv run ruff format . && uv run ruff check . && uv run mypy && uv run pytest -n auto
 ```
 
 The tests need no API keys and no internet connection. Ruff limits each function's complexity, branches and arguments. Split a new function that goes over a limit instead of adding a `noqa`. `pytest` measures coverage and fails below 85% or on any warning. CI also lints the workflows with actionlint and zizmor, and scans the image with Grype; a fixable critical vulnerability fails the build.
diff --git a/pyproject.toml b/pyproject.toml
index 51f8c46..195c151 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -26,6 +26,7 @@ dev = [
     "mypy>=1.18",
     "pytest>=8.4",
     "pytest-cov>=7",
+    "pytest-xdist>=3.8.0",
     "resvg-py>=0.2",
     "ruff>=0.14",
 ]
diff --git a/uv.lock b/uv.lock
index d9c3838..0738658 100644
--- a/uv.lock
+++ b/uv.lock
@@ -140,6 +140,15 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/3f/0c/7a64e1ac90541a8edf50daef0914848011fb057a5bf55284a4811e21939a/coverage-7.16.2-py3-none-any.whl", hash = "sha256:11d28e9123a9156cb405d8d27b44256c9a58fb5decc2073a8f17862057e3aa0f", size = 215754, upload-time = "2026-09-27T12:28:59.075Z" },
 ]
 
+[[package]]
+name = "execnet"
+version = "2.1.2"
+source = { registry = "https://pypi.org/simple" }
+sdist = { url = "https://files.pythonhosted.org/packages/bf/89/780e11f9588d9e7128a3f87788354c7946a9cbb1401ad38a48c4db9a4f07/execnet-2.1.2.tar.gz", hash = "sha256:63d83bfdd9a23e35b9c6a3261412324f964c2ec8dcd8d3c6916ee9373e0befcd", size = 166622, upload-time = "2025-11-12T09:56:37.75Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/ab/84/02fc1827e8cdded4aa65baef11296a9bbe595c474f0d6d758af082d849fd/execnet-2.1.2-py3-none-any.whl", hash = "sha256:67fba928dd5a544b783f6056f449e5e3931a5c378b128bc18501f7ea79e296ec", size = 40708, upload-time = "2025-11-12T09:56:36.333Z" },
+]
+
 [[package]]
 name = "flatbuffers"
 version = "25.12.19"
@@ -404,6 +413,7 @@ dev = [
     { name = "mypy" },
     { name = "pytest" },
     { name = "pytest-cov" },
+    { name = "pytest-xdist" },
     { name = "resvg-py" },
     { name = "ruff" },
 ]
@@ -426,6 +436,7 @@ dev = [
     { name = "mypy", specifier = ">=1.18" },
     { name = "pytest", specifier = ">=8.4" },
     { name = "pytest-cov", specifier = ">=7" },
+    { name = "pytest-xdist", specifier = ">=3.8.0" },
     { name = "resvg-py", specifier = ">=0.2" },
     { name = "ruff", specifier = ">=0.14" },
 ]
@@ -492,6 +503,19 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/9d/7a/d968e294073affff457b041c2be9868a40c1c71f4a35fcc1e45e5493067b/pytest_cov-7.1.0-py3-none-any.whl", hash = "sha256:a0461110b7865f9a271aa1b51e516c9a95de9d696734a2f71e3e78f46e1d4678", size = 22876, upload-time = "2026-03-21T20:11:14.438Z" },
 ]
 
+[[package]]
+name = "pytest-xdist"
+version = "3.8.0"
+source = { registry = "https://pypi.org/simple" }
+dependencies = [
+    { name = "execnet" },
+    { name = "pytest" },
+]
+sdist = { url = "https://files.pythonhosted.org/packages/78/b4/439b179d1ff526791eb921115fca8e44e596a13efeda518b9d845a619450/pytest_xdist-3.8.0.tar.gz", hash = "sha256:7e578125ec9bc6050861aa93f2d59f1d8d085595d6551c2c90b6f4fad8d3a9f1", size = 88069, upload-time = "2025-07-01T13:30:59.346Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/ca/31/d4e37e9e550c2b92a9cbc2e4d0b7420a27224968580b5a447f420847c975/pytest_xdist-3.8.0-py3-none-any.whl", hash = "sha256:202ca578cfeb7370784a8c33d6d05bc6e13b4f25b5053c30a152269fd10f0b88", size = 46396, upload-time = "2025-07-01T13:30:56.632Z" },
+]
+
 [[package]]
 name = "pyyaml"
 version = "6.0.3"