Ast Grep Mcp

ast-grep-mcp is a local stdio Model Context Protocol server that gives agents access to the real ast-grep CLI for structural search, scan, rule testing, and explicitly gated rewrites.

It is designed for agentic coding workflows where text search is not enough and filesystem safety matters.

Features

• Structural search with ast-grep run and JSON results.
• Project scans with ast-grep scan using config files, rule files, inline rules, or filters.
• Rule test execution with ast-grep test.
• Version and binary resolution diagnostics.
• Rewrite preview by default, with mutation gated behind an explicit apply: true input.
• Workspace-relative path validation that rejects absolute paths, .. escapes, and symlinks that resolve outside the workspace.
• No network listener: stdio transport only.

Requirements

• Node.js 20 or newer.
• An MCP client that can launch stdio servers.

The package depends on @ast-grep/cli, which installs the matching platform binary during package installation. You can still override binary resolution with AST_GREP_BIN when needed.

Installation

Use it directly from npm in your MCP client configuration:

{
  "mcpServers": {
    "ast-grep": {
      "command": "npx",
      "args": ["-y", "ast-grep-mcp"],
      "cwd": "/path/to/workspace"
    }
  }
}

Or install it globally:

npm install -g ast-grep-mcp

{
  "mcpServers": {
    "ast-grep": {
      "command": "ast-grep-mcp",
      "cwd": "/path/to/workspace"
    }
  }
}

Set cwd to the workspace the agent should inspect. Tool paths are resolved relative to that workspace.

Tools

Tool	Purpose
ast_grep_search	Runs ast-grep run with structural patterns, optional rewrites, and JSON output.
ast_grep_scan	Runs ast-grep scan with config, rule files, inline rules, filters, and JSON output.
ast_grep_test	Runs ast-grep test for rule suites.
ast_grep_version	Reports the resolved ast-grep binary path, source, and version.

Rewrite Safety

Rewrite-capable requests require an explicit apply value:

{
  "pattern": "$A && $A()",
  "rewrite": "$A?.()",
  "apply": false,
  "lang": "ts",
  "paths": ["src"]
}

• apply: false previews replacements and does not pass --update-all.
• apply: true passes --update-all and applies all replacements or scan rule fixes.
• rewrite requires apply, so callers must explicitly choose preview or mutation.
• apply: true without a rewrite or fix-capable scan request is rejected.

For ast_grep_scan, fixes must be defined in ast-grep rules or config. scan does not accept an ad-hoc rewrite string.

Binary Resolution

The server resolves ast-grep in this order:

1. AST_GREP_BIN
2. ast-grep on PATH
3. sg on PATH, only when sg --version identifies ast-grep
4. The bundled @ast-grep/cli dependency

Use ast_grep_version to confirm which binary the server selected.

Safety Model

• stdio only; no HTTP server or socket listener.
• All file inputs are workspace-relative.
• Absolute paths and .. escapes are rejected.
• Existing symlink components that resolve outside the workspace are rejected.
• Commands use spawn argv arrays with shell: false.
• Interactive ast-grep mode is not exposed.
• Tool calls use timeouts and bounded stdout/stderr buffers.
• Results are returned as JSON text plus MCP structuredContent.

Local Development

pnpm install
pnpm run verify

Useful scripts:

Script	Description
pnpm run dev	Start the MCP server from TypeScript source.
pnpm run build	Clean and build declarations plus the bundled CLI entrypoint.
pnpm run test	Run the Vitest suite.
pnpm run typecheck	Run TypeScript type checking.
pnpm run format:check	Check formatting with oxfmt.
pnpm run lint	Lint with oxlint.
pnpm run verify	Run format, lint, typecheck, tests, and build.
pnpm run pack:dry-run	Build and inspect the npm package contents.

For local MCP development against this repository:

{
  "mcpServers": {
    "ast-grep": {
      "command": "pnpm",
      "args": ["run", "dev"],
      "cwd": "/path/to/ast-grep-mcp"
    }
  }
}

When developing the server itself, launch it from this repository. When using the published package, set cwd to the target workspace.

Release Process

This project uses Changesets and GitHub Actions.

1. Add a changeset with pnpm changeset for user-facing changes.
2. Open a pull request. The PR workflow runs formatting, linting, type checking, tests, build, and an npm pack dry run on Node 20 and 22.
3. Merge to main. The release workflow opens or updates a version PR.
4. Merge the version PR. The release workflow publishes to npm with provenance using NPM_TOKEN.

Repository maintainers need to configure an npm automation token as the NPM_TOKEN GitHub Actions secret.

License

MIT