get-pr-diff

name	get-pr-diff
description	Fetch GitHub pull request diffs with gh CLI, including large-PR fallback strategies.
tools	["Bash"]

Get PR Diff

Skill for fetching GitHub pull request diffs using the gh CLI. Supports normal and large PRs with automatic fallback strategies.

Tools

• Bash

Quick Start

Given a repository (owner/repo) and PR number, use these commands to get the diff.

Strategy 1: Full Diff (try first)

gh pr diff <PR_NUMBER> --repo <OWNER/REPO>

This returns the unified diff for the entire PR. It works for most PRs but will fail with HTTP 406 if the diff exceeds GitHub's 20,000 line limit.

Strategy 2: Per-File Patches (fallback for large PRs)

If the full diff fails or the PR is known to be large, fetch the list of changed files with their individual patches:

gh api "repos/<OWNER/REPO>/pulls/<PR_NUMBER>/files" --paginate -q '.[] | "--- \(.filename) (\(.status), +\(.additions) -\(.deletions))\n\(.patch // "")"'

Note on pagination: GitHub returns at most 30 files per page. The --paginate flag handles this automatically, but for PRs with 300+ files, the response may be very large. In that case, consider reviewing only the most impactful files.

Strategy 3: Individual File Diff (for targeted review)

To fetch the patch for a single file:

gh api "repos/<OWNER/REPO>/pulls/<PR_NUMBER>/files" --paginate -q '.[] | select(.filename == "<FILE_PATH>") | .patch'

Strategy 4: Full File Content (when patch context is insufficient)

To see the full content of a file at the PR's head commit:

gh api "repos/<OWNER/REPO>/contents/<FILE_PATH>?ref=<BRANCH_OR_SHA>" -q '.content' | base64 -d

Handling Large PRs

When dealing with a large PR (many files or a diff that exceeds GitHub's limit):

1. Start with the file list — use Strategy 2 without the patch to get an overview:

   gh api "repos/<OWNER/REPO>/pulls/<PR_NUMBER>/files" --paginate -q '.[] | "\(.filename)\t\(.status)\t+\(.additions)\t-\(.deletions)"'
   

2. Prioritize files for review — focus on:

   • Files with the most changes (high addition/deletion counts)
   • Security-sensitive paths (auth, crypto, config, env)
   • Core business logic (not generated code, lock files, etc.)
   • Files that are added or modified (skip deleted-only files if the deletion is straightforward)

3. Fetch patches for priority files using Strategy 3

4. Use the local clone if available — for understanding broader context, the repository clone (if provided) lets you Read, Grep, and Glob files directly without API calls.

Tips

• The gh CLI is pre-authenticated. No token setup needed.
• All gh api calls support --paginate for multi-page results.
• The -q / --jq flag lets you filter JSON responses inline.
• Patch output from the GitHub API uses unified diff format, same as gh pr diff.