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Add tools to your MCP server.

Before you begin

1. Install agentregistry on Kubernetes.
2. Create an MCP server.

Add a tool

Each tool is a Python file in the src/tools/ directory of your MCP scaffold. The file must import the shared mcp instance from core.server and define at least one function that is decorated with @mcp.tool(). The file is picked up automatically at server startup.

1. Create a new tool file. The following command creates a greeting tool that takes a name as input and returns Hello, {name}!.

   cat > mymcp/src/tools/greet.py << 'EOF'
   from core.server import mcp
   
   @mcp.tool(description="Return a greeting for the given name.")
   def example_greet(name: str) -> str:
       return f"Hello, {name}!"
   EOF

2. Run the server with the MCP Inspector to verify the new tool is available.

   arctl run mymcp --inspector

   Example output:

   → fastmcp-python: docker run --rm -p 3000:3000 localhost:5001/mymcp:latest --transport http --host 0.0.0.0 --port 3000
   2026-05-14 18:39:46,327 - INFO - Loaded tool module: sum
   2026-05-14 18:39:46,329 - INFO - Loaded tool module: echo
   2026-05-14 18:39:46,329 - INFO - Loaded tool module: greet
   2026-05-14 18:39:46,329 - INFO - 📦 Successfully loaded 3 tools
   ...
   INFO     Starting MCP server 'mymcp' with transport 'http' on http://0.0.0.0:3000/mcp
   

3. Connect to your MCP server in the Inspector tool.

   

   

4. Try out the new tool.

   1. Navigate to the Tools tab. Verify that you see the example_echo, example_sum, and example_greet tools.
   2. Select the example_greet tool and enter any name in the name field, such as me.
   3. Click Execute Tool and verify that you see the Hello, me! message.

   

   

5. Exit the MCP Inspector and stop the server by pressing Ctrl+C.

Next