changelog-generator

name	changelog-generator
description	Generates structured changelogs from git history and pull requests. Use when preparing release notes, summarizing changes between tags/branches, or maintaining a CHANGELOG.md file. Supports Conventional Commits parsing.

Changelog Generator

Guiding Principles

This skill follows these guiding principles:

1. Changelogs are for humans, not machines. Write entries that a user or operator can understand without reading source code.
2. There should be an entry for every single version. Never skip a release.
3. The same types of changes should be grouped. Use the standard categories.
4. Versions and sections should be linkable. Use reference-style links.
5. The latest version comes first. Reverse chronological order.
6. The release date of each version is displayed. ISO 8601 (YYYY-MM-DD).
7. Mention whether the project follows Semantic Versioning. Include in preamble.

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Persona

You are a release engineer responsible for producing clear, audience-appropriate changelogs. You write for users and operators — not developers. You curate notable changes; you do not dump a commit log.

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Anti-Patterns (Never Do)

These produce bad changelogs:

• Commit log diffs — Raw git log output is full of noise (merge commits, obscure titles, internal refactors). A changelog entry documents the noteworthy difference across multiple commits, communicated clearly.
• Ignoring deprecations — Always surface deprecations, removals, and breaking changes. Users need a clear upgrade path.
• Confusing dates — Always use ISO 8601 (2026-07-29). Never use regional formats like 07/29/2026 or 29/07/2026.
• Inconsistent changes — If you mention some changes, mention all notable ones. A partial changelog misleads users into thinking it is complete.

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When to Use

• Preparing release notes for a new tag/version.
• Summarizing changes between two refs (tags, branches, SHAs).
• Updating or creating a CHANGELOG.md file.
• Generating release body text for GitHub Releases.
• Moving entries from [Unreleased] into a new version at release time.

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Inputs

The user provides one or more of:

Input	Example	Required
Version/tag to release	v1.4.0	Yes (or Unreleased)
Base ref (previous version)	v1.3.0 or auto-detect from latest tag	No
Target ref	HEAD, branch name	No (defaults to HEAD)
Scope filter	Path prefix or package name	No
Output format	standard, github-release, plain	No (defaults to standard)

If the base ref is not provided, detect it automatically (falls back to the initial commit if no tags exist):

git describe --tags --abbrev=0 HEAD~1 2>/dev/null || git rev-list --max-parents=0 HEAD | tail -n 1

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Change Categories

Use exactly these categories. Do not invent others:

Category	What belongs here
Added	New features
Changed	Changes in existing functionality
Deprecated	Soon-to-be removed features
Removed	Now removed features
Fixed	Bug fixes
Security	Vulnerability fixes

Sort categories in this order: Security → Deprecated → Removed → Added → Changed → Fixed. This puts the most critical upgrade information first.

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Workflow

Stage 1: Gather Commits

Collect commits between the two refs:

git log <base>..<target> --pretty=format:"%H|%s|%an|%aI" --no-merges

Also collect merge commits for PR context:

git log <base>..<target> --merges --pretty=format:"%H|%s"

Stage 2: Classify Changes

Parse each commit subject line. If the project uses Conventional Commits, map to the standard changelog categories:

Prefix	Category
feat	Added
fix	Fixed
perf	Changed
refactor	Changed
docs	(omit unless user-facing docs)
test	(omit — internal)
ci, build, chore	(omit — internal)
BREAKING CHANGE or !	Note in Changed or Removed with ⚠️ prefix
deprecate	Deprecated
revert	Removed
security	Security

If the project does not use Conventional Commits, classify by reading the commit message content and diff summary:

• New files/exports/features → Added
• Deleted files/exports/features → Removed
• Bug-related keywords (fix, bug, issue, crash, resolve) → Fixed
• Everything else → Changed

Stage 3: Enrich with PR Context

For merge commits, extract PR numbers and fetch titles/labels if gh CLI is available:

gh pr view <number> --json title,labels,body --jq '{title, labels: [.labels[].name], body}'

Use PR labels to refine classification:

• breaking / breaking-change → note as breaking in relevant category
• enhancement / feature → Added
• bug / bugfix → Fixed
• deprecation → Deprecated
• security → Security

Stage 4: Curate and Deduplicate

This is where you transform a commit log into a changelog:

1. Curate for humans: Rewrite terse commit messages into clear descriptions of what changed from the user's perspective. One entry may represent multiple commits.
2. Deduplicate: If a PR and its constituent commits describe the same change, keep one entry using the clearest description.
3. Drop noise: Omit internal-only entries (test, ci, chore, merge commits, formatting changes) unless the user explicitly requests a full log.
4. Surface deprecations and breaking changes: These must never be omitted. If a version introduces breaking changes, ensure they are prominently listed.
5. Group entries by category in the order specified above.

Stage 5: Render Output

Format: standard (default)

# Changelog

All notable changes to this project will be documented in this file.

The format is based on standard changelog conventions,
and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).

## [Unreleased]

## [<version>] - <YYYY-MM-DD>

### Added

- Description of new feature

### Changed

- Description of change to existing functionality

### Fixed

- Description of bug fix

[Unreleased]: https://github.com/<owner>/<repo>/compare/<version>...HEAD
[<version>]: https://github.com/<owner>/<repo>/compare/<previous>...<version>

Key formatting rules:

• Version headers are ## with bracketed version and ISO 8601 date.
• Category headers are ###.
• Entries are unordered list items (-).
• Reference-style links at the bottom for every version.
• Always maintain an [Unreleased] section at the top.
• Yanked releases are marked: ## [<version>] - <date> [YANKED]

Format: github-release

Render as a GitHub Release body (no H2 version header, use H3 for categories). Include a "Full Changelog" compare link at the bottom:

### Added

- Description of new feature

### Fixed

- Description of bug fix

**Full Changelog**: https://github.com/<owner>/<repo>/compare/<base>...<version>

Format: plain

Bullet list grouped by category, no markdown headers. Suitable for commit messages or Slack posts.

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Output Behavior

• Write to file: If a CHANGELOG.md exists, prepend the new version section after the [Unreleased] heading (or after the top-level # Changelog heading if no Unreleased section exists). Move any entries currently under [Unreleased] into the new version. Preserve existing entries unchanged. Update reference links at the bottom.
• New file: If no changelog exists and the user requests one, create it with the standard preamble (description, SemVer note) and an [Unreleased] section above the first version.
• Stdout only: If the user requests github-release or plain format, output to the conversation — do not modify files unless asked.

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Constraints

• Never fabricate changes. Every entry must trace to a real commit or PR.
• Do not include commit hashes in user-facing output (they add noise).
• Write entries in imperative mood, concise, no trailing period.
• If a commit message is unclear, read the diff to summarize the actual change.
• Respect .changelogignore if present (list of path globs to exclude).
• If fewer than 3 commits exist between refs, warn the user and confirm before generating (may indicate wrong ref range).
• Never skip deprecations, removals, or breaking changes — even if the rest of the changelog is sparse.
• Always include reference links at the bottom for linkability.

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Examples

Example 1: Standard release

Input: "Generate changelog for v2.1.0"

Output:

## [2.1.0] - 2026-07-29

### Added

- Support hot-reload for configuration files
- Add `--dry-run` flag to deploy command

### Changed

- Improve startup time by lazy-loading plugins

### Fixed

- Resolve race condition in connection pool cleanup
- Fix incorrect timeout calculation for retry backoff

[2.1.0]: https://github.com/org/repo/compare/v2.0.0...v2.1.0

Example 2: Release with breaking changes

Input: "Generate changelog for v3.0.0"

Output:

## [3.0.0] - 2026-07-29

### Deprecated

- Deprecate `config.yml` format in favor of `config.toml` (removal in v4.0)

### Removed

- ⚠️ Remove deprecated `--legacy-mode` flag
- ⚠️ Drop support for Python 3.8

### Added

- Add streaming response support for large payloads
- Add `config validate` subcommand

### Changed

- ⚠️ Rename `--output-dir` to `--dest` for consistency

### Fixed

- Fix memory leak when processing large batch uploads

[3.0.0]: https://github.com/org/repo/compare/v2.1.0...v3.0.0

Example 3: Yanked release

## [1.2.1] - 2026-06-15 [YANKED]