mcp-diff

6 unified-diff tools that Claude/Cursor can actually use. Diff, patch, 3-way merge, summarize. Free, MIT.

The existing MCP servers for diff are either too thin (just diff) or coupled to GitHub Gist + PNG rendering. mcp-diff is the focused text-in/text-out trio — diff, apply patch, three-way merge — plus a few helpers.

Install

{
  "mcpServers": {
    "diff": {
      "command": "npx",
      "args": ["-y", "@dpm-tools/mcp-diff"]
    }
  }
}

Requires Node.js 22.18+.

Tools (6)

• diff — Unified diff between two text strings. Configurable context lines.
• apply_patch — Apply a unified diff to text. Clean error on hunk rejection.
• three_way_merge — diff3-style merge with <<<<<<< / ======= / >>>>>>> conflict markers.
• compare_files — Read two local files (absolute paths only) and diff them.
• summarize_diff — Parse a patch into {lines_added, lines_removed, files_affected, hunk_count, net_change}.
• structured_diff — Line-by-line JSON array of {op, value, line_a, line_b} for LLMs that don't want to parse unified-diff text.

Example prompts

• "Diff these two versions of my function..."
• "Apply this patch to my code and show me the result."
• "Three-way merge: here's the base, here's my version, here's the upstream version."
• "Compare /tmp/old.json and /tmp/new.json — what changed?"
• "Summarize this diff — how many lines added/removed across which files?"

See examples/prompts.md for more.

Why this exists

Claude routinely needs to reason about diffs but struggles to produce or parse them reliably. Existing servers:

• keyhoffman/diff-mcp — just diff, no merge or patch.
• gorosun/unified-diff-mcp — couples diff to GitHub Gist upload + PNG rendering. Overkill.

mcp-diff is the focused trio that handles 95% of real workflows: diff, patch, three-way merge. Plus structured-output mode so LLMs don't parse unified-diff text character-by-character.

Built on the popular diff npm package (MIT, ~1M weekly downloads). MIT, zero telemetry, no API keys.

Safety

• 10 MB input cap per text input (prevents OOM)
• Absolute paths required for compare_files; .. segments rejected
• All errors return isError: true with descriptive messages

Sister servers from dpm

• @dpm-tools/mcp-devkit — 15 dev utilities (UUID, hash, JWT, JSON, cron, color, etc.)
• @dpm-tools/mcp-public-data — sun, moon, holidays, geocoding (zero API keys)

More small, sharp MCP servers shipping weekly.

License

MIT © dpm (digital product mill)