This Lightweight Tool Flags Breaking Changes Before You Ship

In modern Go projects, it's too easy for accidental API changes or subtle documentation edits to sneak through pull requests or release processes unnoticed.

relimpact is a lightweight CLI tool that helps you understand what really changed between two Git refs — with clean, structured, human-friendly reports.

Use it in CI pipelines, release PRs, or locally before tagging new versions.

✨ Features

• 🔍 API Diff — Track breaking public API changes (structs, interfaces, functions, constants, variables).
• 📝 Docs Diff — Section-aware Markdown diff to highlight meaningful content changes.
• 🗂️ Other Files Diff — Group file changes by extension (.sh, .sql, .json, etc.) to surface migrations and auxiliary files.
• 🚀 Designed for Release PR reviews — Quickly see the real impact of changes.
• 🖋️ Markdown Reports — Ready to paste into GitHub Releases, Slack, or changelogs.
• ⚙️ Works in GitHub Actions, GitLab CI, or locally — Integrates easily.
• 🔒 No server required — Pure CLI tool.

🚀 Quickstart

Run on a GitHub PR:

relimpact --old=v1.0.0 --new=HEAD > release-impact.md

Example Output:

⚙️ GitHub Action Integration

name: Release Impact on PR

on:
  pull_request:
    branches: [ master ]
    types: [ opened, synchronize, reopened ]

jobs:
  release-impact:
    name: Generate Release Impact Report
    runs-on: ubuntu-latest

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

      - name: Determine previous tag
        id: prevtag
        run: |
          git fetch --tags
          TAG_LIST=$(git tag --sort=-version:refname)
          PREV_TAG=$(echo "$TAG_LIST" | head -n2 | tail -n1)
          echo "Previous tag: $PREV_TAG"
          # Fallback to first tag if no previous
          if [ -z "$PREV_TAG" ]; then
            PREV_TAG=$(echo "$TAG_LIST" | head -n1)
            echo "Fallback to first tag: $PREV_TAG"
          fi
          echo "prev_tag=$PREV_TAG" >> $GITHUB_OUTPUT

      - name: Determine new ref
        id: newref
        run: |
          if [ "${{ github.event_name }}" = "pull_request" ]; then
            echo "new_ref=${{ github.event.pull_request.head.sha }}" >> $GITHUB_OUTPUT
          else
            echo "new_ref=HEAD" >> $GITHUB_OUTPUT
          fi

      - uses: hashmap-kz/relimpact-action@main
        with:
          old-ref: ${{ steps.prevtag.outputs.prev_tag }}
          new-ref: ${{ steps.newref.outputs.new_ref }}
          output: release-impact.md

      - name: Upload Release Impact Report
        uses: actions/upload-artifact@v4
        with:
          name: release-impact-${{ github.run_id }}-${{ github.run_attempt }}
          path: release-impact.md

📦 Installation

Homebrew

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

Manual Download

👉 Download latest release

🧠 How It Works

1️⃣ Go Source API Changes

• Uses Go type system & AST parsing:
  • Detects breaking changes: method signatures, removed fields, new/removed types, etc.
  • Ignores formatting & comment noise.
  • Based on golang.org/x/tools/go/packages.

2️⃣ Markdown Docs Changes

• Section-aware diff of .md files:
  • Headings added/removed.
  • Links and images changes.
  • Section word count diffs.
  • Based on goldmark parser.

3️⃣ Other Files Changes

• Groups changes by file type:
  • .sql, .sh, .json, .yaml, .conf, etc.
  • Uses git diff --name-status.

Why Use It?

Most release PRs include:

✅ API changes
✅ Doc updates
✅ Migration scripts
✅ Other important config tweaks

But raw git diffis noisy and hard to review.
relimpact gives you a release-ready summary, focusing on what's important.

📜 License

MIT License. See LICENSE.

👉 Try it today: https://github.com/hashmap-kz/relimpact

If you found this useful, leave a ⭐ on GitHub — it helps others discover the project!

Happy releasing 🚀