mcpforge

One English sentence in. A tested, spec-free FastMCP 3.x server out.

mcpforge turns a plain-English description into a complete FastMCP 3.x MCP server — tools, Pydantic input validation, error handling, a pytest suite, run config, and client setup docs — all wired together and ready to inspect, validate, and install. There's no MCP schema or protocol boilerplate to hand-write: the sentence is the spec. You write it; Claude writes the implementation; mcpforge runs the generated test suite and validators before you ever run it.

⚡ 60-second start

You need Python 3.12+, uv, and an Anthropic API key.

uv tool install fastmcp-builder      # or: pip install fastmcp-builder
export ANTHROPIC_API_KEY="your_anthropic_api_key"

mcpforge generate "A weather server that returns today's forecast for a city" -o weather-server

No key yet? Try the demo. mcpforge demo runs the real plan → generate → validate pipeline against a built-in recording and writes a complete, validated weather server — no API key, no spend. It's the fastest way to see exactly what mcpforge produces:

bash

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uvx --from fastmcp-builder mcpforge demo

Bring your own key (BYOK). Generation runs on your Anthropic API key — mcpforge calls the Claude API directly and nothing is proxied through a hosted service. A single generate makes a few model calls (plan → server → tests), so a typical run costs roughly $0.05–$0.30 in API usage on the default model (claude-sonnet-4-6). That figure is an estimate — it scales with server complexity and your chosen model, and is not a live measurement. Everything that doesn't call the model — validate, inspect, list, doctor, and init — is free.

That's the whole loop. mcpforge plans the tools, generates the code, then runs syntax, security, lint, import, and pytest checks against the result — so what lands in ./weather-server/ is already validated:

# weather-server/server.py  (excerpt)
"""Weather forecast MCP server."""

from fastmcp import FastMCP

mcp = FastMCP("Weather")

# Illustrative lookup — describe a real source and mcpforge wires the call for you.
_FORECASTS: dict[str, dict] = {
    "san francisco": {"high_c": 18, "low_c": 12, "summary": "Foggy"},
    "denver": {"high_c": 24, "low_c": 9, "summary": "Clear"},
}


@mcp.tool
async def get_forecast(city: str) -> dict:
    """Return today's forecast for a city."""
    key = city.strip().lower()
    if key not in _FORECASTS:
        raise ValueError(f"No forecast available for {city!r}")
    return {"city": city, **_FORECASTS[key]}


if __name__ == "__main__":
    mcp.run(transport="streamable-http")

Every generation also produces test_server.py (a real pytest suite), pyproject.toml, a README.md, and an MCP client config.json — a complete project, not a snippet. Run it with:

cd weather-server
uv run server.py            # start the server (streamable-http)
uv run pytest -v            # run the generated tests
mcpforge validate .         # re-run the full validation suite anytime

The snippet above is an illustrative toy ("weather") for the docs. Real generations match your description — see examples/ for live generated servers (todo, file reader, database query, Slack notifier, TypeScript).

Build, then audit — the MCP toolkit

mcpforge has a sibling: mcp-audit (mcp-audits on PyPI). They're two halves of one workflow — forge a server, then audit what your agents can actually touch before you trust it.

# build
mcpforge generate "A weather server that returns today's forecast for a city" -o weather-server

# audit everything your agents can reach (read-only, no install needed)
uvx --from mcp-audits mcp-audit scan --ssrf-check

mcp-audit is read-only by default — it never edits a config and reports env-var key names only, never values. Build with confidence, then verify your blast radius.

Registry-ready metadata lives in server.json with the MCP Registry name io.github.saagpatel/mcpforge and PyPI package fastmcp-builder. Treat that metadata as discovery/provenance context, not as proof that generated servers are safe to run without review.

Use as an MCP server

mcpforge is itself an MCP server: point an MCP client (Claude Code, Claude Desktop, Cursor) at it and your agent can forge, validate, and inspect MCP servers inside a conversation. It runs locally over stdio (it writes files into your workspace and calls your model provider on your own key), so it is not offered as a hosted remote.

uvx fastmcp-builder

Add it to a client config (Claude Code shown). generate, update, and plan call the model provider, so set the key in the server env:

{
  "mcpServers": {
    "mcpforge": {
      "command": "uvx",
      "args": ["fastmcp-builder"],
      "env": { "ANTHROPIC_API_KEY": "<your-key>", "MCPFORGE_WORKSPACE": "/path/to/workspace" }
    }
  }
}

Workspace paths are resolved against MCPFORGE_WORKSPACE and confined to it. Note that generate and update write files and incur model-provider cost (roughly $0.05 to $0.30 per call on your key).

Features

• Plain-English generation — describe your server in natural language; Claude writes the implementation
• Complete project scaffold — tools, Pydantic input models, error handling, pyproject.toml, and a pytest suite generated together
• FastMCP 3.x native — output uses modern FastMCP decorators and transport configuration, not raw MCP protocol boilerplate
• Validate before running — mcpforge validate runs syntax, security, lint, import, and pytest checks against generated servers
• Iterate safely — mcpforge update modifies an existing generated server and backs up changed files before writing
• Discover generated servers — mcpforge list finds mcpforge-generated projects in a workspace
• Inspect and diagnose — mcpforge inspect summarizes generated server shape, while mcpforge doctor checks local readiness
• Machine-readable output — status-like commands expose --json for agent workflows
• OpenAPI curation controls — include/exclude tags, operation allowlists, and operation limits keep generated integrations focused
• Scaffold without an LLM — mcpforge init creates a minimal FastMCP server skeleton for local iteration
• MCP server mode — mcpforge-server exposes generation, planning, validation, inspection, doctor, and discovery tools so AI assistants can build safely

More commands

The PyPI distribution is fastmcp-builder; the installed commands are mcpforge and mcpforge-server. Beyond generate:

# See it work with no API key — generate a weather server from a built-in recording
mcpforge demo

# Generate a new MCP server
mcpforge generate "A todo list manager with create, read, update, and delete operations"

# Validate an existing generated server
mcpforge validate ./my-server

# Modify an existing generated server
mcpforge update ./my-server "Add a tool to export todos as CSV"

# Find generated servers in the current workspace
mcpforge list . --recursive

# Inspect a generated server without executing it
mcpforge inspect ./my-server

# Check local prerequisites and provider readiness
mcpforge doctor