Changelog Generator Skill

Generate changelogs from conventional commits for Java projects.

When to Use

Before a release
User says "generate changelog" / "update changelog" / "what changed since last release"
After completing a milestone

Versioning Convention Detection

Detect versioning style using this priority order:

1. Check CLAUDE.md (if exists)

grep -A5 "## Versioning" CLAUDE.md 2>/dev/null

Look for explicit convention:

## Versioning
This project uses Semantic Versioning (x.y.z).
Tag format: `release-x.y.z`

2. Fallback: Detect from git tags

git tag --sort=-version:refname | head -10

Pattern detected	Versioning style
`v3.15.0`, `3.15.0`	SemVer (x.y.z)
`release-3.15.0`	SemVer with prefix
`v2.1`, `2.1`	Two-component (x.y)
`2026.01`, `26.1`	CalVer
No pattern	Ask user

3. Fallback: Detect from CHANGELOG.md

grep -E "^\#+ \[.*\]" CHANGELOG.md | head -5

Extract version format from existing entries.

4. Last resort: Ask user

No versioning convention detected. Which format does this project use?
- Semantic Versioning (x.y.z) - e.g., 3.15.0
- Two-component (x.y) - e.g., 2.1
- Calendar Versioning - e.g., 2026.01

Supported Versioning Styles

Style	Format	Tag examples	Version bump
SemVer	x.y.z	`v3.15.0`, `release-3.15.0`	major.minor.patch
Two-component	x.y	`v2.1`, `2.1`	major.minor
CalVer	YYYY.MM[.patch]	`2026.01`, `2026.01.1`	year.month[.patch]

Legacy Projects (CLAUDE.md without versioning section)

If CLAUDE.md exists but has no versioning info:

Don't assume - detect from tags/changelog

If detected, optionally suggest adding to CLAUDE.md:

Detected versioning: SemVer (x.y.z) with tag prefix 'release-'
Want me to add this to CLAUDE.md for future reference?

Output Format

Supports two formats - detect from existing CHANGELOG.md or ask user preference.

Format A: Keep a Changelog (h2 versions)

# Changelog

## [Unreleased]

## [1.2.0] - 2026-01-29

### Added
- [#123]: New feature for plugin dependencies

### Changed
- [#456]: Improved performance of plugin loading

### Fixed
- [#234]: Resolved NPE when directory missing

Format B: pf4j style (h3 versions)

## Change Log

### [Unreleased][unreleased]

### [3.15.0] - 2026-01-29

#### Added
- [#123]: New feature for plugin dependencies

#### Changed
- [#456]: Improved performance of plugin loading

#### Fixed
- [#234]: Resolved NPE when directory missing

Reference-Style Links (Recommended)

Use reference-style links for cleaner, more readable entries:

#### Fixed
- [#648]: Restore missing `module-info.class` in multi-release JAR
- [#625]: Fix exception handling inconsistency in `startPlugin()`

#### Added
- [#629]: Validate dependency state on plugin start
- [#633]: Allow customization of `PluginClassLoader` parent delegation

<!-- At the bottom of the file -->
[#648]: https://github.com/user/repo/issues/648
[#633]: https://github.com/user/repo/pull/633
[#629]: https://github.com/user/repo/pull/629
[#625]: https://github.com/user/repo/pull/625

Benefits:

Cleaner to read (no long URLs inline)
Links defined once, reusable
Easier to write and maintain

Version Comparison Links

Add comparison links at the bottom for easy diff viewing:

[unreleased]: https://github.com/user/repo/compare/release-3.15.0...HEAD
[3.15.0]: https://github.com/user/repo/compare/release-3.14.1...release-3.15.0
[3.14.1]: https://github.com/user/repo/compare/release-3.14.0...release-3.14.1

Pattern: [version]: https://github.com/{owner}/{repo}/compare/{previous-tag}...{current-tag}

Section Order

Adapt to existing file, or use this default order:

Section	When to use
Fixed	Bug fixes
Changed	Changes to existing functionality
Added	New features
Deprecated	Soon-to-be removed features
Removed	Removed features
Security	Vulnerability fixes (CVEs)

Note: pf4j uses Fixed → Changed → Added → Removed. Keep a Changelog uses Added → Changed → Deprecated → Removed → Fixed → Security.

Rule: Follow existing file's order if present.

Mapping Conventional Commits to Changelog

Commit Type	Changelog Section
feat	Added
fix	Fixed
perf	Changed
refactor	Changed
build(deps)	Changed or Security (if CVE)
BREAKING CHANGE	Changed (with bold note)
deprecate	Deprecated

Workflow

Check for existing CHANGELOG.md
```
cat CHANGELOG.md | head -20
```
Detect format (h2 vs h3 versions, section order, link style).

Determine version range

# Find last tag
git describe --tags --abbrev=0

# List recent tags
git tag --sort=-version:refname | head -5

Get commits since last release
```
git log v3.14.1..HEAD --oneline
```
Extract issue/PR references Look for patterns: #123, fixes #123, closes #123, (#123)
Generate changelog entry
- Group by section
- Use reference-style links
- Add version comparison link
Suggest version bump (based on detected versioning style)

SemVer (x.y.z):
- BREAKING CHANGE → Major (3.0.0 → 4.0.0)
- feat → Minor (3.14.0 → 3.15.0)
- fix only → Patch (3.14.0 → 3.14.1)
Two-component (x.y):
- BREAKING CHANGE → Major (2.0 → 3.0)
- feat/fix → Minor (2.1 → 2.2)
CalVer (YYYY.MM):
- New month → 2026.01 → 2026.02
- Same month, new release → 2026.01 → 2026.01.1

Token Optimization

Use git log --oneline for initial scan
Only fetch full body if BREAKING CHANGE suspected
Reuse existing link definitions from file
Don't re-read entire changelog - just prepend new section

Example: Full Workflow

Input: User says "generate changelog for next release"

Step 1: Check existing format

head -30 CHANGELOG.md

→ Detects pf4j style (h3 versions, Fixed first)

Step 2: Find version range

git describe --tags --abbrev=0

→ release-3.15.0

Step 3: Get commits

git log release-3.15.0..HEAD --oneline

→ 5 commits found

Step 4: Generate entry

### [Unreleased][unreleased]

#### Fixed
- [#650]: Fix memory leak in extension factory

#### Changed
- [#651]: Rename `LegacyExtension*` to `IndexedExtension*`

#### Added
- [#652]: Add support for plugin priority ordering

Step 5: Generate link definitions

[#652]: https://github.com/pf4j/pf4j/pull/652
[#651]: https://github.com/pf4j/pf4j/pull/651
[#650]: https://github.com/pf4j/pf4j/issues/650

Step 6: Update version comparison links

[unreleased]: https://github.com/pf4j/pf4j/compare/release-3.15.0...HEAD

Step 7: Suggest version

Suggested: 3.16.0 (minor - has new feature)

Handling Edge Cases

No conventional commits

List under "Changed" with original message:

#### Changed
- Updated plugin loading mechanism
- Refactored test utilities

Security fix

#### Security
- [#618], [#623]: Fix path traversal vulnerabilities in ZIP extraction

Breaking change

#### Changed
- **BREAKING**: [#645] Renamed `LegacyExtension*` classes to `IndexedExtension*`

Multiple issues for same fix

- [#630], [#631]: Set `failedException` when plugin validation fails

Integration with Existing CHANGELOG.md

Read existing file to detect:
- Heading level (## or ### for versions)
- Section order
- Link style (reference or inline)
- Existing link definitions
Insert new version after [Unreleased] section
Merge link definitions - add new ones, keep existing
Update [unreleased] comparison link to point to new version

Quick Reference

User says	Action
"generate changelog"	Full changelog since last tag
"changelog since v3.14"	From specific version
"what's unreleased"	Preview unreleased changes
"update changelog for 3.16"	Generate and insert for version
"add changelog entry for #123"	Single issue entry