👋 A way to let LLMs speak Just
A production-ready MCP server that provides seamless integration with Just command runner, enabling AI assistants to discover, execute, and introspect Justfile recipes through the standardized MCP protocol.
If it isn't immediately obvious, the benefit of having LLMs use Just vs. bash is that running Just commands (via MCP) provides a context-saving abstraction where they don't need to waste context opening/reading bash files, Python scripts, or other build artifacts. The LLM via MCP simply gets the command, parameters, and hints - it's in their memory as "these are commands available to you."
No more watching LLMs execute just -l to get command lists, inevitably start reading the justfile, then try to write justfile syntax (like it's a Makefile), corrupt the justfile, and create a bad experience. Just's evolving syntax simply doesn't have a large enough corpus in frontier models today - we need more popular repos with justfiles in the training dataset.
Just-mcp is fundamentally safer than bash. If you read HackerNews, there's a story at least once daily about operators whose LLMs start forgetting, hallucinating, and eventually breaking down - deleting files and doing nasty unwanted things. Giving LLMs unsupervised, unrestricted bash access without carefully monitoring context consumption is a recipe for disaster.
Using Justfile fixes that. Even if the LLM modifies its own justfile, the next context is memoized by the justfile (hopefully in an idempotent git repo). This abstraction shields the llm from the command line complexity where hallucinations or attention tracking the current working directory cause it to go over the rails and off the cliff.
Just-mcp is perfect for anybody doing agent execution:
- Ultra-low overhead - probably better than every other tool
- Human-friendly - justfiles are easy for humans and low overhead for LLMs
- Quick and dirty - while some prefer full Python FastAPI servers, just-mcp is just easy-as
- sm0l model friendly - works great with self-hostable GPU/CPU open source models with 8k-32k context limits
Just has useful patterns for introducing:
- Transparent logging without distracting the agent
- Secondary model inspection - use sm0l models to scan commands asking "is this harmful?" before execution
- Python decorator-like patterns for command validation
- Idempotent execution backed by git repos
b00t mcp create just-mcp -- bash just-mcp --stdio "${REPO_ROOT}"
b00t mcp export just-mcp
- 🏗️ Complete MCP Server - Full rmcp 0.3.0 integration with MCP 2024-11-05 protocol
- 📋 Recipe Discovery - Parse and list all available Justfile recipes
- ⚡ Recipe Execution - Execute recipes with parameters and capture structured output
- 🔍 Recipe Introspection - Get detailed recipe information, parameters, and documentation
- ✅ Justfile Validation - Syntax and semantic validation with error reporting
- 🌍 Environment Management - Comprehensive .env file support and variable expansion
- 🧪 Full Test Coverage - 33 passing tests across integration and unit test suites
list_recipes- List all available recipes in the justfilerun_recipe- Execute a specific recipe with optional argumentsget_recipe_info- Get detailed information about a specific recipevalidate_justfile- Validate the justfile for syntax and semantic errors
# Clone and build
git clone <repository-url>
cd just-mcp
cargo build --release
# Test the server
cargo run -- --stdioAdd to your Claude Desktop MCP configuration:
{
"mcpServers": {
"just-mcp": {
"command": "/path/to/just-mcp",
"args": ["--stdio"]
}
}
}# Run as MCP server
just-mcp --stdio
# Run in specific directory
just-mcp --directory /path/to/project --stdio# Run all tests (33 tests)
cargo test
# Run specific test suites
cargo test --test basic_mcp_test # Protocol compliance testing
cargo test --test mcp_integration_working # SDK integration testingbasic_mcp_test.rs- Direct protocol compliance testing using raw JSON-RPCmcp_integration_working.rs- Type-safe SDK integration testing with rmcp client- Unit tests - 25+ tests covering parser, executor, validator, and environment modules
just-mcp/
├── src/main.rs # CLI binary
├── just-mcp-lib/ # Core library
│ ├── parser.rs # Justfile parsing
│ ├── executor.rs # Recipe execution
│ ├── validator.rs # Validation logic
│ ├── environment.rs # Environment management
│ └── mcp_server.rs # MCP protocol implementation
├── tests/ # Integration tests
└── justfile # Demo recipes
- Rust 1.82+ with async/await support
- rmcp 0.3.0 - Official MCP SDK for Rust
- serde/serde_json - JSON serialization
- snafu - Structured error handling
- tokio - Async runtime
- LSP-Style Completion System - Intelligent autocompletion for recipes and parameters
- Enhanced Diagnostics - Advanced syntax error reporting and suggestions
- Virtual File System - Support for stdin, remote sources, and in-memory buffers
- Release Preparation - Documentation, CI/CD, and crate publication
- Plugin system for custom recipe types
- Integration with other build tools
- Performance optimizations for large justfiles
- Advanced dependency visualization
// List available recipes
await client.callTool("list_recipes", {});
// Execute recipe with parameters
await client.callTool("run_recipe", {
"recipe_name": "build",
"args": "[\"--release\"]"
});
// Get recipe information
await client.callTool("get_recipe_info", {
"recipe_name": "test"
});// Validate justfile
await client.callTool("validate_justfile", {
"justfile_path": "./custom.justfile"
});This project follows the b00t development methodology:
- TDD Approach - Tests first, implementation second
- Feature Branches - Never work directly on main branch
- Structured Errors - Use snafu for error management
- Git Workflow - Clean commits with descriptive messages
just build # Build the project
just test # Run tests
just server # Start MCP server
just clean # Clean build artifactsThis project is licensed under LICENSE.
- Installed cocogitto for conventional commit enforcement
- Configured
cog.tomlwith proper commit types and changelog settings - Set up git hooks for commit message linting (
commit-msg) and pre-push testing
- CI Pipeline (
ci.yml): Multi-platform testing (Ubuntu, Windows, macOS), formatting, clippy, commit linting - Release Pipeline (
release.yml): Automated versioning, changelog generation, GitHub releases, and crates.io publishing
- Updated both
Cargo.tomlfiles with complete metadata (description, keywords, categories, license, etc.) - Added proper exclusions for development-only files
- Verified MIT license is in place
- README.md is production-ready with installation and usage instructions
- Created initial
CHANGELOG.mdfor release tracking - Updated
.gitignorewith Rust-specific entries
- All commits must follow conventional commit format (enforced by git hooks)
- Use
feat:,fix:,docs:, etc. prefixes for automatic versioning - Push to
mainbranch triggers automated releases and crates.io publishing - Library tests pass ✅ (25/25) with comprehensive test coverage
- Automated Versioning: Cocogitto analyzes commit messages for semantic versioning
- GitHub Releases: Automatic changelog generation and GitHub release creation
- Crates.io Publishing: Library crate (
just-mcp-lib) publishes first, then binary crate (just-mcp) - CI/CD Pipeline: Multi-platform testing (Ubuntu, Windows, macOS) with formatting and clippy checks
# Install from crates.io
cargo install just-mcp
# Or download from GitHub releases
wget https://github.com/promptexecution/just-mcp/releases/latest/download/just-mcp- Just - The command runner this integrates with
- Model Context Protocol - The protocol specification
- rmcp - Official Rust MCP SDK
- just-vscode - VSCode extension with LSP integration for enhanced Just authoring
- just-awesome-agents - Collection of patterns and tools for agent execution with Just# Test change to trigger pre-push hook
