diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 3092348..0df540d 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -6,7 +6,35 @@ on:
   pull_request:
   workflow_dispatch:
 
+# Install StructKit via the published major tag. v0 exists on
+# httpdss/structkit-setup (same commit as v0.0.1).
+permissions:
+  contents: read
+  actions: write
+
 jobs:
+  test-requires-structkit-on-path:
+    name: Test Requires StructKit on PATH
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v7
+
+      - name: Run without StructKit
+        id: missing
+        continue-on-error: true
+        uses: ./
+        with:
+          command: validate
+
+      - name: Expect PATH error
+        run: |
+          if [[ "${{ steps.missing.outcome }}" != "failure" ]]; then
+            echo "Expected the action to fail when structkit is not on PATH"
+            exit 1
+          fi
+          echo "Missing structkit failed as expected"
+
   test-validate:
     name: Test Validate Command
     runs-on: ubuntu-latest
@@ -14,6 +42,9 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v7
 
+      - name: Set up StructKit
+        uses: httpdss/structkit-setup@v0
+
       - name: Create test structure file
         run: |
           cat > .structkit.yaml << 'EOF'
@@ -35,6 +66,9 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v7
 
+      - name: Set up StructKit
+        uses: httpdss/structkit-setup@v0
+
       - name: Create test structure file
         run: |
           cat > .structkit.yaml << 'EOF'
@@ -64,6 +98,9 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v7
 
+      - name: Set up StructKit
+        uses: httpdss/structkit-setup@v0
+
       - name: Create test structure file
         run: |
           cat > .structkit.yaml << 'EOF'
@@ -94,6 +131,11 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v7
 
+      - name: Set up StructKit from git
+        uses: httpdss/structkit-setup@v0
+        with:
+          structkit-version: "https://github.com/httpdss/structkit.git@main"
+
       - name: Create test structure file
         run: |
           cat > .structkit.yaml << 'EOF'
@@ -102,12 +144,11 @@ jobs:
                 content: "Testing version"
           EOF
 
-      - name: Run with git installation
+      - name: Run with git-installed StructKit
         uses: ./
         with:
           command: validate
           struct_file: .structkit.yaml
-          structkit_version: "https://github.com/httpdss/structkit.git@main"
 
   test-validate-structkit-yaml-fixture:
     name: Test Validate .structkit.yaml Fixture
@@ -116,6 +157,9 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v7
 
+      - name: Set up StructKit
+        uses: httpdss/structkit-setup@v0
+
       - name: Run validate with .structkit.yaml fixture
         uses: ./
         with:
@@ -129,6 +173,9 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v7
 
+      - name: Set up StructKit
+        uses: httpdss/structkit-setup@v0
+
       - name: Run validate with legacy .struct.yaml fixture
         uses: ./
         with:
@@ -142,6 +189,9 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v7
 
+      - name: Set up StructKit
+        uses: httpdss/structkit-setup@v0
+
       - name: Place .structkit.yaml at repo root
         run: cp tests/fixtures/structkit-yaml/.structkit.yaml .structkit.yaml
 
@@ -157,6 +207,9 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v7
 
+      - name: Set up StructKit
+        uses: httpdss/structkit-setup@v0
+
       - name: Place legacy .struct.yaml at repo root
         run: cp tests/fixtures/legacy-struct-yaml/.struct.yaml .struct.yaml
 
@@ -172,6 +225,9 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v7
 
+      - name: Set up StructKit
+        uses: httpdss/structkit-setup@v0
+
       - name: Place both default files at repo root
         run: |
           cp tests/fixtures/structkit-yaml/.structkit.yaml .structkit.yaml
@@ -189,6 +245,9 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v7
 
+      - name: Set up StructKit
+        uses: httpdss/structkit-setup@v0
+
       - name: Run validate without config
         id: validate
         continue-on-error: true
diff --git a/CHANGELOG.md b/CHANGELOG.md
new file mode 100644
index 0000000..b9a7fa1
--- /dev/null
+++ b/CHANGELOG.md
@@ -0,0 +1,25 @@
+# Changelog
+
+All notable changes to this project are documented in this file.
+
+## Unreleased
+
+### Breaking changes
+
+- **This action no longer installs Python or StructKit.** It expects `structkit` to already be on `PATH`.
+- Removed inputs `structkit_version` and `python_version`.
+- Call [`httpdss/structkit-setup`](https://github.com/httpdss/structkit-setup) first when you need StructKit installed:
+
+  ```yaml
+  - uses: httpdss/structkit-setup@v0
+  - uses: httpdss/structkit-action@v0
+    with:
+      command: validate
+  ```
+
+  If `structkit` is missing, the action fails with an error that points at `uses: httpdss/structkit-setup@v0`.
+- Docs, examples, and CI pin the published major tags `@v0` (`httpdss/structkit-setup@v0`, then `httpdss/structkit-action@v0`). Show `structkit-version` on setup when you need a specific StructKit release.
+
+### License
+
+- Relicensed from MIT to Apache License 2.0.
diff --git a/LICENSE b/LICENSE
index 66f5f2f..d645695 100644
--- a/LICENSE
+++ b/LICENSE
@@ -1,21 +1,202 @@
-MIT License
-
-Copyright (c) 2026 Kenneth Belitzky
-
-Permission is hereby granted, free of charge, to any person obtaining a copy
-of this software and associated documentation files (the "Software"), to deal
-in the Software without restriction, including without limitation the rights
-to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-copies of the Software, and to permit persons to whom the Software is
-furnished to do so, subject to the following conditions:
-
-The above copyright notice and this permission notice shall be included in all
-copies or substantial portions of the Software.
-
-THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-SOFTWARE.
+
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diff --git a/README.md b/README.md
index 33871e7..17f714e 100644
--- a/README.md
+++ b/README.md
@@ -4,6 +4,8 @@
 
 Companion to [StructKit](https://github.com/httpdss/structkit). Run `validate`, `generate`, or a dry-run drift check as a workflow step. Star the [core repo](https://github.com/httpdss/structkit).
 
+**Breaking change:** this action no longer installs Python or StructKit. Add [`httpdss/structkit-setup@v0`](https://github.com/httpdss/structkit-setup) first (see [CHANGELOG](CHANGELOG.md)).
+
 ## Features
 
 - 🔍 **Validate** structure definitions on every PR
@@ -11,7 +13,7 @@ Companion to [StructKit](https://github.com/httpdss/structkit). Run `validate`,
 - 🔄 **Drift Detection** - detect when generated files don't match definitions
 - 🛡️ **Safe Defaults** - runs with `--no-hooks` and `--non-interactive` by default
 - 📦 **Custom Structures** - supports external structure repositories
-- 🎯 **Flexible Versioning** - install from PyPI, git, or specific versions
+- 🔧 **Bring your own StructKit** - install with [`httpdss/structkit-setup`](https://github.com/httpdss/structkit-setup) (or any other method) before this action runs
 
 ## Quick Start
 
@@ -26,7 +28,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v7
-      - uses: httpdss/structkit-action@v1
+      - uses: httpdss/structkit-setup@v0
+      - uses: httpdss/structkit-action@v0
         with:
           command: validate
 ```
@@ -44,7 +47,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v7
-      - uses: httpdss/structkit-action@v1
+      - uses: httpdss/structkit-setup@v0
+      - uses: httpdss/structkit-action@v0
         with:
           command: generate
           dry_run: true
@@ -66,8 +70,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v7
+      - uses: httpdss/structkit-setup@v0
 
-      - uses: httpdss/structkit-action@v1
+      - uses: httpdss/structkit-action@v0
         with:
           command: generate
           struct_file: .structkit.yaml
@@ -93,13 +98,11 @@ jobs:
 | `diff` | Show diff of changes (use with dry_run for drift detection) | No | `false` |
 | `no_hooks` | Disable hooks during execution (requires StructKit >= 3.3.0) | No | `false` |
 | `non_interactive` | Run in non-interactive mode (check if your StructKit version supports this flag) | No | `false` |
-| `structkit_version` | StructKit version to install (version number, `latest`, or git URL) | No | `latest` |
 | `structures_path` | Path to custom structures directory | No | `''` |
 | `structures_repository` | Custom structures repository to checkout (format: `owner/repo`) | No | `''` |
 | `structures_repository_path` | Path within structures_repository where structures are located | No | `structures` |
 | `structures_repository_ref` | Git ref (branch/tag/commit) to checkout from structures_repository | No | `main` |
 | `extra_args` | Additional arguments to pass to StructKit command | No | `''` |
-| `python_version` | Python version to use | No | `3.x` |
 | `fail_on_diff` | Fail the action if changes would be made (drift detection) | No | `false` |
 
 ## Outputs
@@ -116,39 +119,46 @@ jobs:
 This repository uses automated release management with semantic versioning:
 
 - **Release Drafting**: Releases are automatically drafted when PRs are merged to main
-- **First Release**: Will be tagged as `v1.0.0`
-- **Major Version Tags**: When a release like `v1.2.3` is published, the major tag `v1` is automatically created/moved to point to it
+- **First Release**: Will be tagged as `v0.0.1`
+- **Major Version Tags**: When a release like `v0.0.1` is published, the major tag `v0` is automatically created/moved to point to it
 - **Pinning Recommendations**:
-  - Use `@v1` to automatically get minor and patch updates (recommended for most users)
-  - Use `@v1.0.0` to pin to a specific version
+  - Use `@v0` to automatically get minor and patch updates (recommended for most users)
+  - Use `@v0.0.1` to pin to a specific version
 
-The major version tag (`v1`) is maintained automatically, so users can always reference the latest stable v1.x.x release using `@v1`.
+The major version tag (`v0`) is maintained automatically, so users can always reference the latest stable v0.x.x release using `@v0`.
 
 
 ## Advanced Examples
 
-### Use Specific StructKit Version
+### Pin the StructKit version
+
+Version selection lives in [`httpdss/structkit-setup`](https://github.com/httpdss/structkit-setup), not this action:
 
 ```yaml
-- uses: httpdss/structkit-action@v1
+- uses: httpdss/structkit-setup@v0
+  with:
+    structkit-version: "3.3.0"
+- uses: httpdss/structkit-action@v0
   with:
     command: validate
-    structkit_version: "1.2.3"
 ```
 
 ### Install from Git
 
 ```yaml
-- uses: httpdss/structkit-action@v1
+- uses: httpdss/structkit-setup@v0
+  with:
+    structkit-version: "https://github.com/httpdss/structkit.git@main"
+- uses: httpdss/structkit-action@v0
   with:
     command: generate
-    structkit_version: "https://github.com/httpdss/structkit.git@main"
 ```
 
 ### Use Custom Structures Repository
 
 ```yaml
-- uses: httpdss/structkit-action@v1
+- uses: httpdss/structkit-setup@v0
+- uses: httpdss/structkit-action@v0
   with:
     command: generate
     structures_repository: myorg/my-structures
@@ -159,7 +169,8 @@ The major version tag (`v1`) is maintained automatically, so users can always re
 ### Generate with Extra Arguments
 
 ```yaml
-- uses: httpdss/structkit-action@v1
+- uses: httpdss/structkit-setup@v0
+- uses: httpdss/structkit-action@v0
   with:
     command: generate
     extra_args: "--verbose --force"
@@ -168,7 +179,8 @@ The major version tag (`v1`) is maintained automatically, so users can always re
 ### Use Action Outputs
 
 ```yaml
-- uses: httpdss/structkit-action@v1
+- uses: httpdss/structkit-setup@v0
+- uses: httpdss/structkit-action@v0
   id: structkit
   with:
     command: generate
@@ -196,7 +208,8 @@ jobs:
           - config/frontend.structkit.yaml
     steps:
       - uses: actions/checkout@v7
-      - uses: httpdss/structkit-action@v1
+      - uses: httpdss/structkit-setup@v0
+      - uses: httpdss/structkit-action@v0
         with:
           command: validate
           struct_file: ${{ matrix.struct_file }}
@@ -217,7 +230,7 @@ If you need automatic PR creation, use the [reusable workflow](https://github.co
 
 ## Requirements
 
-- Python 3.x (automatically installed by the action)
+- `structkit` on `PATH` (install with [`httpdss/structkit-setup@v0`](https://github.com/httpdss/structkit-setup) first, or any other method)
 - GitHub Actions runner with bash support
 
 ## Configuration file
@@ -230,11 +243,12 @@ This action is designed to work with different versions of StructKit. Some comma
 
 ## How It Works
 
-1. **Setup** - Installs Python and StructKit
-2. **Checkout** - Optionally checks out custom structures repository
-3. **Execute** - Runs the specified StructKit command
-4. **Outputs** - Provides execution results for downstream steps
-5. **Cleanup** - Removes temporary files
+1. **Require StructKit** - Fails with a clear error if `structkit` is not on `PATH`
+2. **Resolve** - Auto-detects `.structkit.yaml` or legacy `.struct.yaml` unless `struct_file` is set
+3. **Checkout** - Optionally checks out a custom structures repository
+4. **Execute** - Runs the specified StructKit command
+5. **Outputs** - Provides execution results for downstream steps
+6. **Cleanup** - Removes temporary files
 
 ## Common Patterns
 
@@ -251,7 +265,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v7
-      - uses: httpdss/structkit-action@v1
+      - uses: httpdss/structkit-setup@v0
+      - uses: httpdss/structkit-action@v0
         with:
           command: validate
 ```
@@ -269,7 +284,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v7
-      - uses: httpdss/structkit-action@v1
+      - uses: httpdss/structkit-setup@v0
+      - uses: httpdss/structkit-action@v0
         with:
           command: generate
           dry_run: true
@@ -290,8 +306,9 @@ jobs:
     environment: production
     steps:
       - uses: actions/checkout@v7
+      - uses: httpdss/structkit-setup@v0
 
-      - uses: httpdss/structkit-action@v1
+      - uses: httpdss/structkit-action@v0
         with:
           command: generate
 
@@ -307,15 +324,15 @@ jobs:
 
 ### Command Not Found
 
-If `structkit` command is not found, ensure Python is properly set up:
+This action does not install StructKit. Add setup first:
 
 ```yaml
-- uses: actions/setup-python@v5
-  with:
-    python-version: '3.x'
-- uses: httpdss/structkit-action@v1
+- uses: httpdss/structkit-setup@v0
+- uses: httpdss/structkit-action@v0
 ```
 
+Or install StructKit yourself (pip, uv, etc.) so `structkit` is on `PATH` before this step.
+
 ### Permission Denied
 
 When using `structures_repository`, ensure your workflow has access:
@@ -335,11 +352,12 @@ Contributions are welcome! Please feel free to submit a Pull Request.
 
 ## License
 
-MIT License - see [LICENSE](LICENSE) file for details.
+Apache License 2.0 - see [LICENSE](LICENSE).
 
 ## Related Projects
 
 - [StructKit](https://github.com/httpdss/structkit) - The main StructKit project
+- [structkit-setup](https://github.com/httpdss/structkit-setup) - Install StructKit in GitHub Actions
 - [StructKit Reusable Workflow](https://github.com/httpdss/structkit/blob/main/.github/workflows/struct-generate.yaml) - Full workflow with PR creation
 
 ## Support
diff --git a/action.yml b/action.yml
index 16bea89..6c94c8e 100644
--- a/action.yml
+++ b/action.yml
@@ -34,10 +34,6 @@ inputs:
     description: 'Run in non-interactive mode (check if your StructKit version supports this flag)'
     required: false
     default: 'false'
-  structkit_version:
-    description: 'StructKit version to install (PyPI version number, "latest", or git URL)'
-    required: false
-    default: 'latest'
   structures_path:
     description: 'Path to custom structures directory (leave empty for default)'
     required: false
@@ -58,10 +54,6 @@ inputs:
     description: 'Additional arguments to pass to StructKit command'
     required: false
     default: ''
-  python_version:
-    description: 'Python version to use'
-    required: false
-    default: '3.x'
   fail_on_diff:
     description: 'Fail the action if changes would be made (drift detection)'
     required: false
@@ -84,6 +76,17 @@ outputs:
 runs:
   using: 'composite'
   steps:
+    - name: Require StructKit on PATH
+      shell: bash
+      run: |
+        if ! command -v structkit >/dev/null 2>&1; then
+          echo "::error::structkit is not on PATH. Add a prior step that installs it, for example:"
+          echo "::error::  uses: httpdss/structkit-setup@v0"
+          echo "::error::This action no longer installs Python or StructKit."
+          exit 1
+        fi
+        echo "Using structkit at $(command -v structkit)"
+
     - name: Resolve struct file
       id: resolve-struct-file
       shell: bash
@@ -94,27 +97,6 @@ runs:
         echo "Using struct file: ${STRUCT_FILE}"
         echo "struct_file=${STRUCT_FILE}" >> "${GITHUB_OUTPUT}"
 
-    - name: Set up Python
-      uses: actions/setup-python@v5
-      with:
-        python-version: ${{ inputs.python_version }}
-
-    - name: Install StructKit
-      shell: bash
-      run: |
-        if [[ "${{ inputs.structkit_version }}" == "latest" ]]; then
-          echo "Installing StructKit from PyPI (latest)"
-          pip install structkit
-        elif [[ "${{ inputs.structkit_version }}" == http* ]]; then
-          echo "Installing StructKit from git URL: ${{ inputs.structkit_version }}"
-          pip install "git+${{ inputs.structkit_version }}"
-        else
-          echo "Installing StructKit version: ${{ inputs.structkit_version }}"
-          pip install "structkit==${{ inputs.structkit_version }}"
-        fi
-        echo "StructKit installed successfully"
-        structkit --help > /dev/null
-
     - name: Checkout custom structures repository
       if: inputs.structures_repository != ''
       uses: actions/checkout@v7
diff --git a/examples/README.md b/examples/README.md
index 5c72f53..1685521 100644
--- a/examples/README.md
+++ b/examples/README.md
@@ -20,7 +20,8 @@ cp examples/validate-pr.yml .github/workflows/
 
 ## Customization Tips
 
-- Replace version pins (`@v1`) with specific commit SHAs for production use
+- Add `httpdss/structkit-setup@v0` before this action so `structkit` is on `PATH`
+- Replace version pins (`@v0`) with specific commit SHAs for production use
 - Adjust `struct_file` paths to match your repository structure (default is `.structkit.yaml`; legacy `.struct.yaml` is still auto-detected if you omit the input)
 - Configure branch names and PR settings according to your workflow
 - Add environment-specific secrets if using private structure repositories
diff --git a/examples/custom-structures.yml b/examples/custom-structures.yml
index eb7f303..9212da3 100644
--- a/examples/custom-structures.yml
+++ b/examples/custom-structures.yml
@@ -16,8 +16,11 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@v7
 
+      - name: Set up StructKit
+        uses: httpdss/structkit-setup@v0
+
       - name: Generate with custom structures
-        uses: httpdss/structkit-action@v1
+        uses: httpdss/structkit-action@v0
         with:
           command: generate
           struct_file: .structkit.yaml
diff --git a/examples/drift-detection.yml b/examples/drift-detection.yml
index 7e67a8a..d3f7c63 100644
--- a/examples/drift-detection.yml
+++ b/examples/drift-detection.yml
@@ -14,9 +14,12 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@v7
 
+      - name: Set up StructKit
+        uses: httpdss/structkit-setup@v0
+
       - name: Check for drift
         id: drift-check
-        uses: httpdss/structkit-action@v1
+        uses: httpdss/structkit-action@v0
         with:
           command: generate
           struct_file: .structkit.yaml
diff --git a/examples/generate-and-commit.yml b/examples/generate-and-commit.yml
index 530c43c..8533094 100644
--- a/examples/generate-and-commit.yml
+++ b/examples/generate-and-commit.yml
@@ -19,8 +19,11 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@v7
 
+      - name: Set up StructKit
+        uses: httpdss/structkit-setup@v0
+
       - name: Generate structure
-        uses: httpdss/structkit-action@v1
+        uses: httpdss/structkit-action@v0
         with:
           command: generate
           struct_file: ${{ github.event.inputs.struct_file || '.structkit.yaml' }}
diff --git a/examples/scheduled-check.yml b/examples/scheduled-check.yml
index 8f5fac9..3e0a411 100644
--- a/examples/scheduled-check.yml
+++ b/examples/scheduled-check.yml
@@ -14,10 +14,13 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@v7
 
+      - name: Set up StructKit
+        uses: httpdss/structkit-setup@v0
+
       - name: Check for drift
         id: drift
         continue-on-error: true
-        uses: httpdss/structkit-action@v1
+        uses: httpdss/structkit-action@v0
         with:
           command: generate
           struct_file: .structkit.yaml
diff --git a/examples/validate-pr.yml b/examples/validate-pr.yml
index adda388..ef2d7e4 100644
--- a/examples/validate-pr.yml
+++ b/examples/validate-pr.yml
@@ -16,8 +16,11 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@v7
 
+      - name: Set up StructKit
+        uses: httpdss/structkit-setup@v0
+
       - name: Validate structure
-        uses: httpdss/structkit-action@v1
+        uses: httpdss/structkit-action@v0
         with:
           command: validate
           struct_file: .structkit.yaml