relimpact

Fast API compatibility reports for Go projects.

relimpact compares two Git refs, snapshots the exported Go API, and reports what changed: breaking changes first, compatible additions below.

It is not a raw diff tool or a changelog generator. It answers one release question:

Did this change break public Go API?

---

Preview

Breaking Changes

New API

PR comment

Install

Using Go:

go install github.com/hashmap-kz/relimpact@latest

Using Homebrew:

brew tap hashmap-kz/homebrew-tap
brew install relimpact

Or download a binary from the Releases page.

Usage

Markdown output is the default:

relimpact --old=v1.0.0 --new=HEAD > api-report.md

HTML output:

relimpact --old=v1.0.0 --new=HEAD --format=html > api-report.html

Run against another repository:

relimpact --dir=/path/to/repo --old=v1.0.0 --new=HEAD

Use maximum concurrency:

relimpact --old=v1.0.0 --new=HEAD --greedy

GitHub Actions

Generate a Markdown report and post it as a pull request comment:

name: API compatibility

on:
  pull_request:
    branches: [ master ]

permissions:
  contents: read
  pull-requests: write

jobs:
  relimpact:
    runs-on: ubuntu-latest

    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0

      - uses: actions/setup-go@v5
        with:
          go-version: "1.25"

      - name: Install relimpact
        run: |
          go install github.com/hashmap-kz/relimpact@latest

      - name: Generate Markdown API report
        run: |
          relimpact \
            --old="${{ github.event.pull_request.base.sha }}" \
            --new="${{ github.event.pull_request.head.sha }}" \
            --format=markdown \
            > api-report.md

      - name: Comment API report on PR
        uses: marocchino/sticky-pull-request-comment@v2
        with:
          header: relimpact-api-report
          recreate: true
          path: api-report.md

To also keep the HTML report as a CI artifact:

      - name: Upload HTML API report
        run: |
          relimpact \
            --old="${{ github.event.pull_request.base.sha }}" \
            --new="${{ github.event.pull_request.head.sha }}" \
            --format=html \
            > api-report.html

      - name: Upload HTML artifact
        uses: actions/upload-artifact@v4
        with:
          name: api-report
          path: api-report.html

License

MIT License. See LICENSE for details.