Content
# ast-grep MCP Server
An experimental [Model Context Protocol (MCP)](https://modelcontextprotocol.io/) server that provides AI assistants with powerful structural code search capabilities using [ast-grep](https://ast-grep.github.io/).
## Overview
This MCP server enables AI assistants (like Cursor, Claude Desktop, etc.) to search and analyze codebases using Abstract Syntax Tree (AST) pattern matching rather than simple text-based search. By leveraging ast-grep's structural search capabilities, AI can:
- Find code patterns based on syntax structure, not just text matching
- Search for specific programming constructs (functions, classes, imports, etc.)
- Write and test complex search rules using YAML configuration
- Debug and visualize AST structures for better pattern development
## Prerequisites
1. **Install ast-grep**: Follow [ast-grep installation guide](https://ast-grep.github.io/guide/quick-start.html#installation)
```bash
# macOS
brew install ast-grep
nix-shell -p ast-grep
cargo install ast-grep --locked
```
2. **Install uv**: Python package manager
```bash
curl -LsSf https://astral.sh/uv/install.sh | sh
```
3. **MCP-compatible client**: Such as Cursor, Claude Desktop, or other MCP clients
## Installation
1. Clone this repository:
```bash
git clone https://github.com/ast-grep/ast-grep-mcp.git
cd ast-grep-mcp
```
2. Install dependencies:
```bash
uv sync
```
3. Verify ast-grep installation:
```bash
ast-grep --version
```
## Running with `uvx`
You can run the server directly from GitHub using `uvx`:
```bash
uvx --from git+https://github.com/ast-grep/ast-grep-mcp ast-grep-server
```
This is useful for quickly trying out the server without cloning the repository.
## Configuration
### For Cursor
Add to your MCP settings (usually in `.cursor-mcp/settings.json`):
```json
{
"mcpServers": {
"ast-grep": {
"command": "uv",
"args": ["--directory", "/absolute/path/to/ast-grep-mcp", "run", "main.py"],
"env": {}
}
}
}
```
### For Claude Desktop
Add to your Claude Desktop MCP configuration:
```json
{
"mcpServers": {
"ast-grep": {
"command": "uv",
"args": ["--directory", "/absolute/path/to/ast-grep-mcp", "run", "main.py"],
"env": {}
}
}
}
```
### Custom ast-grep Configuration
The MCP server supports using a custom `sgconfig.yaml` file to configure ast-grep behavior.
See the [ast-grep configuration documentation](https://ast-grep.github.io/guide/project/project-config.html) for details on the config file format.
You can provide the config file in two ways (in order of precedence):
1. **Command-line argument**: `--config /path/to/sgconfig.yaml`
2. **Environment variable**: `AST_GREP_CONFIG=/path/to/sgconfig.yaml`
## Usage
This repository includes comprehensive ast-grep rule documentation in [ast-grep.mdc](https://github.com/ast-grep/ast-grep-mcp/blob/main/ast-grep.mdc). The documentation covers all aspects of writing effective ast-grep rules, from simple patterns to complex multi-condition searches.
You can add it to your cursor rule or Claude.md, and attach it when you need AI agent to create ast-grep rule for you.
The prompt will ask LLM to use MCP to create, verify and improve the rule it creates.
## Features
The server provides four main tools for code analysis:
### 🔍 `dump_syntax_tree`
Visualize the Abstract Syntax Tree structure of code snippets. Essential for understanding how to write effective search patterns.
**Use cases:**
- Debug why a pattern isn't matching
- Understand the AST structure of target code
- Learn ast-grep pattern syntax
### 🧪 `test_match_code_rule`
Test ast-grep YAML rules against code snippets before applying them to larger codebases.
**Use cases:**
- Validate rules work as expected
- Iterate on rule development
- Debug complex matching logic
### 🎯 `find_code`
Search codebases using simple ast-grep patterns for straightforward structural matches.
**Parameters:**
- `max_results`: Limit number of complete matches returned (default: unlimited)
- `output_format`: Choose between `"text"` (default, ~75% fewer tokens) or `"json"` (full metadata)
**Text Output Format:**
```
Found 2 matches:
path/to/file.py:10-15
def example_function():
# function body
return result
path/to/file.py:20-22
def another_function():
pass
```
**Use cases:**
- Find function calls with specific patterns
- Locate variable declarations
- Search for simple code constructs
### 🚀 `find_code_by_rule`
Advanced codebase search using complex YAML rules that can express sophisticated matching criteria.
**Parameters:**
- `max_results`: Limit number of complete matches returned (default: unlimited)
- `output_format`: Choose between `"text"` (default, ~75% fewer tokens) or `"json"` (full metadata)
**Use cases:**
- Find nested code structures
- Search with relational constraints (inside, has, precedes, follows)
- Complex multi-condition searches
## Usage Examples
### Basic Pattern Search
Use Query:
> Find all console.log statements
AI will generate rules like:
```yaml
id: find-console-logs
language: javascript
rule:
pattern: console.log($$$)
```
### Complex Rule Example
User Query:
> Find async functions that use await
AI will generate rules like:
```yaml
id: async-with-await
language: javascript
rule:
all:
- kind: function_declaration
- has:
pattern: async
- has:
pattern: await $EXPR
stopBy: end
```
## Supported Languages
ast-grep supports many programming languages including:
- JavaScript/TypeScript
- Python
- Rust
- Go
- Java
- C/C++
- C#
- And many more...
For a complete list of built-in supported languages, see the [ast-grep language support documentation](https://ast-grep.github.io/reference/languages.html).
You can also add support for custom languages through the `sgconfig.yaml` configuration file. See the [custom language guide](https://ast-grep.github.io/guide/project/project-config.html#languagecustomlanguage) for details.
## Troubleshooting
### Common Issues
1. **"Command not found" errors**: Ensure ast-grep is installed and in your PATH
2. **No matches found**: Try adding `stopBy: end` to relational rules
3. **Pattern not matching**: Use `dump_syntax_tree` to understand the AST structure
4. **Permission errors**: Ensure the server has read access to target directories
## Contributing
This is an experimental project. Issues and pull requests are welcome!
## Related Projects
- [ast-grep](https://ast-grep.github.io/) - The core structural search tool
- [Model Context Protocol](https://modelcontextprotocol.io/) - The protocol this server implements
- [FastMCP](https://github.com/pydantic/fastmcp) - The Python MCP framework used
- [Codemod MCP](https://docs.codemod.com/model-context-protocol) - Gives AI assistants tools like tree-sitter AST and node types, ast-grep instructions (YAML and JS ast-grep), and Codemod CLI commands to easily build, publish, and run ast-grep based codemods.
[](https://mseep.ai/app/ast-grep-ast-grep-mcp)
