🦀 Rust Builder MCP Server

An autonomous Model Context Protocol (MCP) server designed to build, debug, and maintain Rust projects.

This is a Meta-MCP Server: It is specifically architected to help LLMs (like Claude) build other MCP servers. It provides the AI with "eyes" to understand code structure, "hands" to safely edit files, and a "brain" containing verified MCP patterns.

⚡ Key Features

✅ Offline Intelligence:

• Zero-Latency Search: Built-in vector search for local Rust documentation (std, etc.) without API calls.
• Local Registry: Queries the local ~/.cargo cache for crate versions and features.

✅ Autonomous Development Workflow:

• "Golden Workflow": Enforces a strict Check → Git Save → Edit → Verify loop.
• Cargo Integration: Autonomously runs check, test, fmt, clippy, and add (dependencies).

✅ Advanced Tooling:

• AST Analysis: Parses Rust code to understand huge files (structs/traits) using minimal tokens.
• Surgical Editing: Uses patch_file logic to modify code precisely without overwriting whole files.
• Meta-Scaffolding: Generates boilerplate for new MCP Tools, Prompts, and Resources automatically.

---

🛠️ Tool Suite

The server exposes a comprehensive set of tools to the LLM:

Category	Tool	Description
👀 Eyes	search_rust_docs	Search local documentation (TF-IDF).
	analyze_code	Parse file AST to see structs, fields, and signatures.
	read_file	Read files with line numbers for precise editing.
	get_project_structure	Visualize the file tree (ignoring target/git).
✋ Hands	patch_file	Edit code safely (handles whitespace normalization).
	scaffold_new_tool	Create new MCP tool boilerplate & mod.rs entries.
	add_dependency	Run cargo add with feature selection.
🧠 Brain	get_mcp_template	Retrieve verified rmcp code patterns.
	explain_error	Get rustc --explain output for error codes.
🛡️ Safety	check_code	Run cargo check --message-format=json.
	run_tests	Run cargo test (with optional filtering).
	git_operations	Commit, Diff, Status, or Undo changes.

---

🚀 Installation

1. Prerequisites

Ensure Rust is installed and the documentation component is available:

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
rustup component add rust-docs

2. Build the Server

git clone https://github.com/CeeArEx/mcp-rust-builder.git
cd mcp-rust-builder
cargo build --release

3. Configure Client

For Claude Desktop (~/Library/Application Support/Claude/claude_desktop_config.json on macOS):

{
  "mcpServers": {
    "rust-builder": {
      "command": "/ABSOLUTE/PATH/TO/mcp-rust-builder/target/release/mcp-rust-builder",
      "args": []
    }
  }
}

For OpenCode / VS Code (Generic):

{
  "mcpServers": {
    "rust-builder": {
      "command": "/ABSOLUTE/PATH/TO/mcp-rust-builder/target/release/mcp-rust-builder",
      "transport": "stdio"
    }
  }
}

---

💡 Usage Examples

Scenario 1: Developing a new Tool

User: "Create a new tool called weather_fetcher that takes a city name."

Agent Action:

1. scaffold_new_tool(name="weather_fetcher", ...) -> Creates file & updates mod.rs.
2. add_dependency(crate="reqwest", ...) -> Adds HTTP client.
3. patch_file(...) -> Implements logic in the new file.
4. check_code() -> Verifies compilation.

Scenario 2: Debugging

User: "Why is my build failing?"

Agent Action:

1. check_code() -> Returns error JSON (e.g., Error E0308).
2. explain_error(code="E0308") -> Reads compiler explanation.
3. read_file(...) -> Reads the specific lines causing the error.
4. patch_file(...) -> Fixes the types.

Scenario 3: Research

User: "How do I use std::fs::File?"

Agent Action:

1. search_rust_docs(query="std::fs::File") -> Returns local HTML documentation summary.

---

📂 Project Structure

mcp-rust-builder/
├── src/
│   ├── main.rs              # Entry point & Tool Router wiring
│   ├── tools/
│   │   ├── mod.rs           # Tool registration
│   │   ├── analyzer.rs      # AST Parsing (syn/quote)
│   │   ├── surgeon.rs       # Smart File Patching
│   │   ├── search_docs.rs   # TF-IDF Search Engine
│   │   ├── scaffolder.rs    # Code Generation
│   │   ├── git.rs           # Version Control
│   │   ├── testing.rs       # Test Runner
│   │   └── ... (other tools)
│   └── utils/
│       └── paths.rs         # System discovery
├── Cargo.toml
└── README.md

🔧 Troubleshooting

• "Rust docs not installed": Run rustup component add rust-docs.
• "Git remote error": Ensure you have a git repo initialized. The server expects a .git folder in the working directory to perform safety saves.
• "Connection Timeout": The initial documentation indexing happens in the background. If the server is slow to start, ensure search_docs.rs is using tokio::spawn.

📄 License

MIT