If you are tired of copy-pasting file paths and line numbers into chat windows to tell your AI coding agent where it messed up, Diffsmith might be your new favorite tool. Released for macOS on September 30, 2026, this $5.99 native application provides a dedicated studio for reviewing local git changes made by any existing AI assistant. It is not another cloud-based review platform; it is a local-first utility designed to keep your code and comments on your machine.

The Local-First Review Workflow

Diffsmith operates entirely within the macOS ecosystem, requiring version 15.0 or later. The core functionality revolves around opening local git repositories and viewing diffs against HEAD, staged changes, specific commits, or branches. The interface supports side-by-side or inline layouts with syntax highlighting and expandable context. A standout feature for rapid iteration is live re-diffing; as files change on disk, the view updates automatically without requiring a manual refresh. This eliminates the friction of constantly switching between a terminal and an IDE to see what an agent just wrote.

Bridging the Gap with MCP

The tool’s real power lies in how it hands feedback back to the AI. Users can click any line to leave anchored comments, which are then compiled into a perfectly formatted prompt with code context via a one-click copy feature. For those using Model Context Protocol (MCP) compatible agents, Diffsmith includes an optional, loopback-only local MCP server. When enabled, your coding agent can read your inline comments and reply directly within the app, creating a closed-loop feedback system without leaving the editor environment. Agent-generated comments are visually distinct from human ones to avoid confusion during intense review sessions.

Privacy and Pricing Model

In an era of subscription fatigue and data harvesting, Diffsmith takes a refreshing stance. It is a one-time purchase for lifetime access, and the developer, Mergeable Pty Ltd, explicitly states that no data is collected. The app is fully sandboxed and makes no outbound network calls unless you explicitly enable the local MCP server. This 'private by design' architecture ensures that your proprietary code and review comments never leave your local machine, addressing a major concern for developers working on sensitive projects.

Key Takeaways

  • Diffsmith is a native macOS app for reviewing AI-generated git diffs locally.
  • It supports MCP integration, allowing agents to read and reply to comments in-app.
  • The tool is a one-time $5.99 purchase with no data collection or cloud dependencies.
  • Live re-diffing and anchored line comments streamline the human-in-the-loop workflow.

The Bottom Line

Diffsmith solves a critical friction point in AI-assisted coding by bringing professional-grade review tools to the local machine, making it a must-have for developers who prioritize privacy and workflow efficiency.