mcp-server-builder

MCP Server Builder

Use this skill when a user asks to create, generate, or build an MCP server. OmniHarness can scaffold a fully functional FastMCP server from a description, write the source code, and run it through the automated test pipeline.

Workflow

1. Understand the intent — identify the server name, description, template type, and any external services or secrets needed.
2. Scaffold the code — write server.py using FastMCP following the template below. Each tool must have a clear docstring and typed parameters.
3. Submit for testing — call mcp_build(server_id=..., source_code=...). The tool runs static security scans, checks that all required secrets are stored in the vault, starts the server in an isolated subprocess, connects the MCP client, lists the discovered tools, and test-calls each one.
4. Report results — tell the user which tools were discovered, which test-calls passed, and whether any secrets are missing.
5. Iterate — if errors are returned fix the code and call mcp_build again.

Do NOT write files to the sandbox for this skill. Pass the complete source code directly to mcp_build as the source_code parameter.

Project structure

A minimal MCP server consists of a single server.py file.

server.py          ← entrypoint — always named server.py
requirements.txt   ← optional — any extra pip packages beyond fastmcp

server.py skeleton

import os

from mcp.server.fastmcp import FastMCP

mcp = FastMCP("server-name")


@mcp.tool()
def tool_name(param: str) -> str:
    """One-sentence description of what this tool does and what it returns."""
    # implementation
    return result


if __name__ == "__main__":
    _transport = os.environ.get("MCP_TRANSPORT", "stdio")
    if _transport == "sse":
        mcp.settings.host = "0.0.0.0"
        mcp.settings.port = int(os.environ.get("MCP_PORT", "8080"))
        mcp.settings.transport_security = None
        mcp.run(transport="sse")
    else:
        mcp.run()