Ummon Code Semantics
The semantic layer for software engineering: Connect code to meaning, build on understanding
What is Ummon Code Semantics?
Ummon Code Semantics is a Model Context Protocol (MCP) server that allows AI assistants like Claude, Cursor, and VS Code to semantic layer for software engineering: connect code to meaning, build on understanding
The semantic layer for software engineering: Connect code to meaning, build on understanding
This server falls under the Developer Tools category on MCPgee, the world's largest MCP server directory with 33,000+ servers.
Features
- The semantic layer for software engineering: Connect code to
Use Cases
Maintainer
Works with
Installation
Manual Installation
npx ummonConfiguration
Configuration Details
claude_desktop_config.json
Performance
Response Metrics
Resource Usage
How to Set Up and Use Ummon Code Semantics
Ummon is a semantic code intelligence tool that builds a knowledge graph of your codebase by indexing functions, classes, and their relationships across Rust, Python, JavaScript, and Java source files. It exposes an MCP server that AI assistants can query to find relevant files for a proposed change, search code by natural language or structured query, and extract domain model concepts from the implementation. Developers use it to give AI coding assistants deep, queryable understanding of large codebases without pasting entire files into context.
Prerequisites
- Rust toolchain (cargo) for installing from crates.io
- OPENROUTER_API_KEY for LLM-powered natural language queries and domain extraction
- A codebase in Rust, Python, JavaScript, or Java to index
- An MCP-compatible client such as Claude Desktop or Cursor
Install Ummon via cargo
Install the ummon binary from crates.io using cargo. This compiles and installs the binary to your cargo bin directory.
cargo install ummonSet the OpenRouter API key
Ummon uses OpenRouter to access LLMs for natural language query understanding and domain model extraction. Export your API key.
export OPENROUTER_API_KEY=your-openrouter-api-keyIndex your codebase
Run ummon index pointing at your project root. Use --full for a complete rebuild, or run without it for incremental updates.
ummon index /path/to/your/codebaseTest queries from the command line
Verify the index works by running a natural language query or a structured query before connecting an AI client.
ummon query "show all authentication functions"
ummon query "select functions where name like 'auth%'" --no-llmStart the MCP server and configure your client
Add Ummon to your Claude Desktop configuration. Ummon exposes its capabilities via MCP so AI assistants can call the query and file-suggestion tools directly.
Ummon Code Semantics Examples
Client configuration
Add this to your claude_desktop_config.json. Set OPENROUTER_API_KEY and adjust the codebase path as needed.
{
"mcpServers": {
"ummon": {
"command": "ummon",
"args": ["serve", "--path", "/path/to/your/codebase"],
"env": {
"OPENROUTER_API_KEY": "your-openrouter-api-key"
}
}
}
}Prompts to try
Once Ummon is connected to your AI client, use these prompts to explore your codebase semantically.
- "Which files are most relevant to fixing the authentication token validation logic?"
- "Show me all functions related to database connection management"
- "What are the main domain concepts in this codebase?"
- "Find all error handling code across the project"
- "Suggest files I should look at to add a new payment method"Troubleshooting Ummon Code Semantics
Natural language queries return no results or fail
Ensure OPENROUTER_API_KEY is set and valid. Natural language queries require LLM access via OpenRouter. Use --no-llm flag for structured queries that do not require an API key.
Index is empty or missing files
Run ummon index /path/to/codebase --full to force a complete rebuild. Ensure the path points to the actual source root and contains supported language files (.rs, .py, .js, .java).
cargo install ummon fails to compile
Ensure your Rust toolchain is up to date by running rustup update stable. Ummon requires a recent stable Rust version.
Frequently Asked Questions about Ummon Code Semantics
What is Ummon Code Semantics?
Ummon Code Semantics is a Model Context Protocol (MCP) server that semantic layer for software engineering: connect code to meaning, build on understanding It connects AI assistants to external tools and data sources through a standardized interface.
How do I install Ummon Code Semantics?
Follow the installation instructions on the Ummon Code Semantics GitHub repository. Clone the repo, install dependencies, and add the server config to your AI client.
Which AI clients work with Ummon Code Semantics?
Ummon Code Semantics works with all major MCP-compatible AI clients including Claude Desktop, Claude Code, Cursor, VS Code (GitHub Copilot), Windsurf, and Cline.
Is Ummon Code Semantics free to use?
Yes, Ummon Code Semantics is open source and available under the Apache-2.0 license. You can use it freely in both personal and commercial projects.
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Set Up Ummon Code Semantics in Your Editor
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Quick Config Preview
Add this to your claude_desktop_config.json or .cursor/mcp.json
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