mermaidiff

mermaidiff turns a code change into a short brief: a sequence diagram of only the steps that changed. Type /mermaidiff on a commit, staged change, GitHub PR or GitLab MR and see the impact in under 30 seconds. ➕ new, ✏️ changed, ➖ removed.

Key Features

• Flow diff: a sequence diagram with only the affected steps, colored by change type. Unchanged steps are collapsed.
• Summary from the diff: the one-line summary comes from the code, not the commit message. If the commit or PR text claims something the diff doesn't do, it says so.
• Proof for every step: each step has a file:line reference and a tier: 🟢 verified, 🔵 seen in code, 🟡 inferred.
• Payload diff: shows changed request, response, event or model fields and the step that uses them.
• Proven breaks only: a 🔴 break is shown only with file:line and proof it's reachable. At most 2 open questions.
• No false positives: a wrong warning is worse than a missing one. If it can't prove it, it doesn't claim it.

Install

git clone https://github.com/osmangoninahid/mermaidiff && cd mermaidiff && ./install.sh

Opens the brief as a standalone HTML page in your browser, with a Copy for MR button.

Supported

• GitHub PRs and GitLab MRs: uses gh / glab if you're logged in, otherwise reads the PR/MR head with plain git.
• Runs as a skill in Claude Code. Codex support is experimental.
• Any language: it reads the diff and finds callers with CodeGraph, Graphify or grep.

Commands

/mermaidiff                     # auto: staged → unstaged → last commit
/mermaidiff staged              # staged changes only
/mermaidiff <PR or MR link>     # someone else's PR / MR
/mermaidiff <commit hash>       # one commit
/mermaidiff main..feature       # a range
/mermaidiff ABC-123             # ticket mode (experimental)

Feedback

Found a wrong claim in a brief? Open an issue with the brief and the commit or PR link.

MIT licensed. Not affiliated with the Mermaid project.