mathews-tom/changelog-composer

Changelog Composer

Transforms raw git history and PR descriptions into polished, audience-appropriate changelogs. Parses conventional commits, classifies changes by impact category, filters internal-only modifications, and produces structured release notes with PR links — following Keep a Changelog conventions.

Reference Files

| File | Contents | Load When | | ------------------------------------ | ------------------------------------------------------------------ | ------------------------------------ | | references/conventional-commits.md | Commit type parsing, scope extraction, breaking change indicators | Repository uses conventional commits | | references/categorization-rules.md | Change classification logic, audience filtering, severity ordering | Always | | references/audience-filter.md | User-facing vs internal change detection, exclusion patterns | Always | | references/changelog-formats.md | Keep a Changelog, GitHub Releases, announcement copy templates | Format selection needed |

Prerequisites

• git — access to the repository history
• gh (optional) — GitHub CLI for PR description extraction
• A tagging strategy (semver tags) for identifying release boundaries

Workflow

Phase 1: Gather Raw Changes

Collect all changes between the previous release and the current state:

1. Identify boundaries — Find the last release tag: git describe --tags --abbrev=0. If no tags exist, use the initial commit or a user-specified starting point.
2. Extract commits — git log <last-tag>..HEAD --oneline --no-merges
3. Extract PR titles — gh pr list --state merged --base main --search "merged:>YYYY-MM-DD" or parse merge commit messages.
4. Parse conventional commits — If the repository follows conventional commits (feat:, fix:, docs:, etc.), extract type, scope, and description. See references/conventional-commits.md.
5. Collect breaking change indicators — Look for BREAKING CHANGE: in commit bodies, ! after type (feat!:), or explicit annotations in PR descriptions.

Phase 2: Classify Changes

Categorize each change by its impact:

| Category | Conventional Commit Type | Indicators | | ---------------- | ----------------------------------------------- | ---------------------------------------------- | | Breaking Changes | feat!:, BREAKING CHANGE: | API removal, signature change, behavior change | | Features | feat: | New capability, new endpoint, new command | | Fixes | fix: | Bug correction, error handling improvement | | Performance | perf: | Speed improvement, memory reduction | | Documentation | docs: | README, API docs, guides | | Internal | chore:, ci:, refactor:, test:, build: | No user-facing impact |

For repositories without conventional commits, classify by reading the commit message and changed files. Code changes to public API → Feature or Fix. Test-only changes → Internal.

Phase 3: Filter for Audience

1. Exclude internal changes by default:

   • CI/CD configuration changes
   • Test additions/modifications
   • Dependency bumps (unless security-relevant)
   • Code refactoring with no behavior change
   • Build system changes

2. Include internal changes only when:

   • They represent significant architecture shifts users should know about
   • They affect development workflow (contributing guide changes)
   • The changelog targets developers, not end-users

3. Highlight breaking changes prominently — always at the top, always with migration guidance.

Phase 4: Compose Entries

For each included change, write a human-readable description:

1. Lead with the impact — "Users can now..." or "Fixed issue where..."
2. Be specific — "Reduced memory usage by 40% for large file processing" not "Performance improvements"
3. Include migration guidance for breaking changes — what the user must change
4. Link to source — PR number, issue number, or commit hash

Phase 5: Output

Assemble the changelog in the requested format, ordered by severity:

1. Breaking Changes (always first)
2. Features
3. Fixes
4. Performance
5. Documentation

Output Format

## [{version}] - {YYYY-MM-DD}

### Breaking Changes
- **`function_name` parameter renamed** — `old_param` is now `new_param`.
  Migration: find/replace `old_param=` with `new_param=` in all call sites. ([#{pr}]({url}))

### Features
- **{Feature name}** — {What it enables and why it matters}. ([#{pr}]({url}))

### Fixes
- Fixed {symptom} when {condition}. ([#{pr}]({url}))

### Performance
- {Operation} is now {X}x faster / uses {X}% less memory. ([#{pr}]({url}))

### Documentation
- Added {guide/reference} for {topic}. ([#{pr}]({url}))

Configuring Scope

| Mode | Input | Output | When to Use | | --------- | -------------------------- | ------------------------ | ----------------------------- | | release | Tag-to-HEAD | Full changelog entry | Preparing a versioned release | | sprint | Date range or commit range | Summary of changes | Sprint review, status update | | pr | Single PR | One-line changelog entry | PR description template |

Calibration Rules

1. User impact first. Every entry should answer "what does this mean for the user?" not "what did the developer do?"
2. Breaking changes are non-negotiable. Never omit or bury breaking changes. They go first, with migration guidance.
3. Specific over vague. "Fixed login timeout on slow connections" beats "Fixed bug." "Added CSV export for reports" beats "New feature."
4. Link everything. Every entry links to its source PR or issue. Users who want details can follow the link.
5. Exclude noise. Internal refactoring, dependency bumps, and CI changes do not belong in user-facing changelogs unless they have user-visible impact.

Error Handling

| Problem | Resolution | | ------------------------------------------- | -------------------------------------------------------------------------------------------------- | | No tags exist in repository | Ask for a starting commit or date. Default to the initial commit if the repository is small. | | Repository doesn't use conventional commits | Classify by reading commit messages and changed files. Note reduced classification accuracy. | | PR descriptions are empty or low-quality | Fall back to commit messages. Flag entries that may need manual review. | | Ambiguous change classification | Default to "Features" for additions, "Fixes" for modifications. Mark uncertain entries for review. | | Too many changes for a single release | Group by component/module. Consider whether the release should be split. | | Merge commits obscure individual changes | Use --no-merges to skip merge commits. Parse individual commits within merged PRs. |

When NOT to Compose

Push back if:

• The user wants to auto-publish release notes without review — changelogs require human judgment
• The repository has no meaningful commit history (single "initial commit" with everything)
• The request is for marketing copy, not technical release notes — different skill
• The changes are not yet merged — changelog is for shipped changes, not in-progress work