Diff Explain

Explain a diff in plain, conversational English. Focus on what changed and why it likely changed, not just listing modified files.

Determine the Diff Source

Parse $ARGUMENTS to determine what diff to explain:

Argument	Command
(none)	git diff (unstaged changes)
--staged	git diff --staged
--unstaged	git diff
A number (e.g., 123)	gh pr diff 123
A commit hash	git show <hash>
A branch name	git diff main...<branch>
Two refs (e.g., v1.0..v1.1)	git diff <ref1>...<ref2>

Gather Context

1. Get the diff using the appropriate command above
2. Get the file list: git diff --stat (or equivalent for the source)
3. If it's a PR, also fetch: gh pr view <number> --json title,body,labels

Explain the Changes

Structure the explanation as:

Overview

One paragraph: what is this change about at a high level? What problem does it solve or what feature does it add?

Key Changes

For each logically grouped change:

• What: which files changed and what was modified
• Why: infer the motivation from the code context
• How: brief description of the implementation approach

Group related file changes together (e.g., "Updated the User model and its tests" rather than listing each file separately).

Notable Details

Flag anything interesting:

• Breaking changes or API modifications
• New dependencies added
• Configuration changes
• Files deleted or renamed
• Potential risks or things a reviewer should look closely at

Summary Stats

Files changed: N
Insertions: +N
Deletions: -N

Guidelines

• Be conversational, not mechanical. "Added a retry mechanism to the HTTP client" is better than "Modified http_client.ts lines 45-60"
• Infer intent from the code. If a function was renamed from getData to fetchUserProfile, note that the rename improves clarity, don't just say "renamed function"
• Highlight the important parts. A 500-line diff might have one key architectural decision — find it and lead with it
• Note what's missing if relevant: "This adds the API endpoint but doesn't include tests yet"
• Skip boilerplate: don't explain auto-generated changes, lock file updates, or formatting-only diffs unless they're the entire change