Diff Anything MCP Server

Diff Anything MCP

Use the installed Diff Anything command line from an MCP client to compare local files, folders, and API schemas. The optional npm package runs over stdio as a child process of your client.

Requirements and setup

• Node.js 22 or newer on macOS or Windows.
• An installed Diff Anything app with its command line. Install the app from the product page. On Windows, the Microsoft Store version provides the command line through its diff-anything.exe app execution alias. On a Mac, the Mac App Store version is sandboxed and cannot read files named on a command line, so install the free Diff Anything command-line helper, which installs /usr/local/bin/diff-anything.
• Folder and API schema comparisons require Diff Anything Pro. The CLI checks the app's locally cached entitlement; open the desktop app to purchase or restore Pro. The Free CLI permits plain-text and JSON comparisons, subject to its daily and file-size limits.
• check_api_compatibility requires a CLI whose help includes --fail-on breaking. Discovery checks the installed binary; an older app returns update_required for this tool.

Your MCP client starts the server with npx, which downloads the pinned version on first use; nothing else needs installing. In Claude Code:

claude mcp add diff-anything -e DIFF_ANYTHING_ROOTS='["/Users/you/Comparisons"]' -- npx -y @grunersoftware/diff-anything-mcp@0.1.0

In clients configured with JSON, the server entry is:

{
  "mcpServers": {
    "diff-anything": {
      "command": "npx",
      "args": ["-y", "@grunersoftware/diff-anything-mcp@0.1.0"],
      "env": { "DIFF_ANYTHING_ROOTS": "[\"/Users/you/Comparisons\"]" }
    }
  }
}

To run without fetching from npm at startup, install a pinned version globally and use the diff-anything-mcp command instead:

npm install --global @grunersoftware/diff-anything-mcp@0.1.0

Set DIFF_ANYTHING_ROOTS in your client's server configuration to a JSON array of existing absolute directories that the server may compare. Until this is configured, only discovery works. Start with a dedicated directory containing files you intend to share with your client.

macOS discovery checks the command-line helper at /usr/local/bin/diff-anything, then /Applications/Diff Anything.app/Contents/MacOS/diff-anything, the same bundle in ~/Applications, and absolute entries on PATH. A Mac App Store copy of the app is skipped, because its own executable cannot read the files; without the helper, tools return helper_required with the helper's download page. Windows discovery checks %LOCALAPPDATA%\Microsoft\WindowsApps\diff-anything.exe and PATH. The Microsoft Store package declares that app execution alias; enable it in Windows settings if it is disabled. For a direct install or another location, set DIFF_ANYTHING_CLI to the absolute executable path. Never use a shell command or arguments in that variable.

VS Code

For a workspace configuration, create .vscode/mcp.json:

{
  "servers": {
    "diff-anything": {
      "type": "stdio",
      "command": "diff-anything-mcp",
      "env": {
        "DIFF_ANYTHING_ROOTS": "[\"/Users/you/Comparisons\"]"
      }
    }
  }
}

If your client cannot find the global command, use the absolute path to Node as command and the absolute path to the installed package's src/index.mjs as the single entry in args. This also avoids Windows clients that cannot directly launch npm's .cmd shim. npm root --global identifies the global package directory.

Clients using mcpServers

For a client such as Claude Code that accepts a project .mcp.json, use the same server entry under mcpServers. This Windows example launches Node directly:

{
  "mcpServers": {
    "diff-anything": {
      "command": "C:\\Program Files\\nodejs\\node.exe",
      "args": ["C:\\Users\\you\\AppData\\Roaming\\npm\\node_modules\\@grunersoftware\\diff-anything-mcp\\src\\index.mjs"],
      "env": {
        "DIFF_ANYTHING_ROOTS": "[\"C:\\\\Users\\\\you\\\\Comparisons\"]"
      }
    }
  }
}

Replace example paths with your actual installation and comparison directories. Restart or reload the server in your client, then call discover_capabilities first. Setup references: VS Code MCP configuration and MCP SDK host setup.

Tools

Example input:

{"left":"/Users/you/Comparisons/before.json","right":"/Users/you/Comparisons/after.json"}

Exit 1 is a completed comparison result, not a server failure. For file and folder comparisons it sets countedDifferences; for API checks it makes compatibilityCheckPassed false. Review the CLI report and its warnings: a failed compatibility check can mean a breaking or unclassified change. A comparison is not proof that a backup is complete or an API is compatible in every respect.

The wrapper returns the CLI report without rewriting its values or removing its masking. There are no tool arguments for raw CLI flags, disabling masking, overriding Pro, merging, batch manifests or writing report files. Errors use isError with a code such as missing_app, helper_required, pro_required, update_required, outside_roots, timeout or output_limit and the CLI's explanation where available.

Local processing and permissions

Diff Anything performs its comparisons locally and sends none of your data to an AI model. The npm wrapper has no hosted runtime, account, API key, HTTP listener or required network connection at runtime. Installing packages requires registry access; launching the installed package directly avoids an npm fetch at startup.

Your MCP client controls what happens to returned tool output. Comparison results can include filenames, paths, document content and changed values. A client may send that output to its model provider or store it. Configure that client's data handling and tool approvals before comparing sensitive files. Existing CLI masking is not a universal secret scanner.

Tools leave compared files unchanged. The CLI can update its local free-comparison usage ledger and read its cached Pro entitlement. The server inherits your process permissions and environment. Allowed roots validate resolved input paths, including symlinks. Folder inputs are scanned before comparison and reject nested symbolic links, junctions and special files, because the CLI can follow links. This validation is capped at 100,000 entries and 60 seconds per tree. These are application-level guards, not an OS sandbox or protection against another process changing files during a comparison. Use local, stable directories; network mounts or cloud placeholders may perform I/O through the operating system.

Each CLI invocation has a 60-second timeout and a combined stdout/stderr limit of 1 MiB. Output beyond the limit is discarded and the process is stopped; a partial report is never presented as complete. One tool request runs at a time; overlapping requests return busy. Client cancellation stops the active CLI child. Large comparisons should be narrowed into smaller pairs.

Development

npm ci
npm test
npm pack

Tests exercise the actual MCP stdio transport with a fixture CLI, argument validation, platform discovery paths, allowed roots, symlink escape rejection, Pro errors, cancellation and output limits. A real installed app is needed to verify platform packaging and entitlement behavior end to end.