SCM Commit Message Tool — VS Code Extension

A lightweight VS Code extension that exposes Language Model tools so that GitHub Copilot's agent mode can automatically read and update the Source Control (Git) commit message input box.

Features

Update modes

When the input box is empty, all modes behave identically — they simply set the message.

Iterative session support

In a typical Copilot agent session the agent may make multiple rounds of changes. Because the default mode is append, each subsequent call adds a new paragraph describing the latest changes while preserving the earlier description. The result is a growing, complete commit message that reflects the entire session.

Requirements

• VS Code ≥ 1.95.0
• Git extension (vscode.git) — built into VS Code
• GitHub Copilot extension with agent mode enabled

Installation

From source

git clone https://github.com/jonasjoest/VSCode-Copilot-autofill-commit-message.git
cd VSCode-Copilot-autofill-commit-message
npm install
npm run compile
npm run package          # produces scm-commit-message-tool-0.1.0.vsix
code --install-extension scm-commit-message-tool-0.1.0.vsix --force

Manual (from .vsix)

npm install
npm run compile
npx @vscode/vsce package --no-dependencies
code --install-extension scm-commit-message-tool-*.vsix --force

Usage with Copilot Agent Mode

Once installed, the tools appear automatically in Copilot's agent mode tool list. Add instructions to your project's .github/copilot-instructions.md to tell the agent to call the tool after making code changes.

No manual invocation is needed — the agent handles everything.

Copilot Instructions Example

Add the following to your .github/copilot-instructions.md:

## SCM Commit Message (MUST Follow)

**CRITICAL - MUST:**
- **After making code changes, ALWAYS update the SCM commit message** using the
  `scm-commit-message-tool_updateCommitMessage` tool
- Call the tool with a concise, **conventional-commit-style** message describing
  the changes just made (e.g., `feat(backend): add invoice validation endpoint`)
- Use the **default `append` mode** so that earlier descriptions from the same
  session are preserved — never use `replace` unless explicitly consolidating
- For multi-step sessions, call the tool after **each logical group of changes**
  rather than once at the very end
- Before updating, you MAY call `scm-commit-message-tool_getCommitMessage` to
  read the current message and avoid duplicating content

Example agent flow

1. Agent makes code changes.
2. Agent calls scm-commit-message-tool_updateCommitMessage with a concise message like feat(backend): add invoice validation endpoint.
3. If the agent makes more changes, it calls the tool again — the new description is appended to the existing message.
4. When the session is complete the SCM input box contains a full description of all changes, ready to commit.

Releasing

Releases are automated via the Release workflow. When a GitHub release is published the workflow builds the extension and attaches the .vsix file to the release automatically.

Steps to create a new release

1. Bump the version in package.json (follow semver):

   npm version patch   # or minor / major
   git push && git push --tags
   

2. Create and publish the release on GitHub:

   • Go to the repository's Releases page and click Draft a new release.
   • Choose the tag you just pushed (e.g. v0.2.0).
   • Fill in the release title and description.
   • Click Publish release.

3. Wait for the workflow to finish. The workflow (triggered by the release: published event) compiles the extension, packages it into a .vsix file, and uploads it as a release asset automatically.

4. Verify the .vsix file appears as an asset on the release page.

Note: The GITHUB_TOKEN secret is automatically provided by GitHub Actions — no additional secrets need to be configured.

Development

npm run watch    # recompile on changes

Reload the VS Code window (Developer: Reload Window) to pick up changes after recompilation.

How it works

The extension uses the stable vscode.lm.registerTool API (available since VS Code 1.93) and declares the tools in package.json under contributes.languageModelTools. When Copilot's agent requests a tool call, VS Code activates the extension and invokes the corresponding tool implementation which accesses the Git extension's Repository.inputBox.value property.

License

MIT — see LICENSE for details.