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fast_mcp_template

fast_mcp_template

by ayushneo
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fast_mcp_template

This is a GitHub template repository. Click Use this template → Create a new repository on github.com/ayushneo/fast_mcp_template, or:

gh repo create my-service --template ayushneo/fast_mcp_template --private --clone

Same layered CRUD/Docker/Poetry base as fastapi_template, plus one thing: the app's own REST endpoints are exposed as MCP tools via fastapi_mcp, so an MCP client (Claude Desktop, Claude Code, any agent framework) can call them directly. Generate a new repository from this template; delete items once you've read how the wiring works.

Built by reading the actual fastapi_mcp source (its README's own code sample is thinner than what's needed to get filtering/auth/transport right), not from the surveyed blog posts — see "What was actually useful" below for why most of those added nothing beyond fastapi_mcp's own docs.

File structure

Identical to fastapi_template/ (see that README for the full layout and its own trade-offs table — those still apply here) plus:

fast_mcp_template/
├── app/
│   ├── core/
│   │   └── mcp.py          -- NEW: builds + mounts the MCP server over this app's own routes
│   ├── api/v1/
│   │   └── items.py         -- CHANGED: explicit operation_id on every route (see why below)
│   └── schemas/
│       └── item.py           -- CHANGED: Field(..., description=...) on every field
└── tests/
    └── test_mcp.py             -- NEW: asserts the exposed tool set, no live MCP session needed

Related MCP server: openapi-mcp

The one architectural choice that matters here

There are two different things "add MCP to a FastAPI app" can mean:

(a) Expose the individual REST endpoints as MCP tools and let an external MCP client do the reasoning about which to call, in what order — this is what fastapi_mcp is actually built for (turn API endpoints into tools, not wrap an agent), and what this template does.

(b) Wrap an internal agent loop as one meta-tool (ask_agent(question) that reasons internally and returns a final answer) — simpler to wire, but hides all tool-selection structure from the client; from the outside it's one opaque tool.

This template builds (a). Notably, this repo already made and recorded the exact same call independently, for the hand-rolled (non-fastapi_mcp) version of this same decision, in react_mcp_server/react-mcp-server-spec.md — same reasoning, arrived at twice without cross-referencing.

Trade-offs specific to the MCP layer

(General FastAPI trade-offs — models vs. schemas, error handling, pagination, logging — are the same as fastapi_template and not repeated here.)

Decision

Options

Chosen, and why

operation_id

Auto-generated (function name + path hash) vs. explicit on every route

Explicit, always — fastapi_mcp uses operation_id as the MCP tool's name. Leave it auto and an unrelated refactor (renaming the function, moving the router) silently renames or breaks the tool from an agent's perspective. The single most-repeated warning across every fastapi_mcp write-up surveyed.

Tool descriptions

Minimal vs. Field(..., description=...) on every schema field

Detailed — this is the entire quality signal an MCP client (an LLM) has to decide whether/how to call a tool. There's no separate "tool doc" to write; the Pydantic field description is the doc.

Transport

mount_sse() (legacy Server-Sent Events) vs. mount_http() (Streamable HTTP)

HTTP — the current, non-deprecated transport (verified against fastapi_mcp's own source, not just its README). Use SSE only if a specific client you must support hasn't moved off it.

Exposure surface

Expose every endpoint vs. filter

Filtered — delete_item is excluded via exclude_operations in app/core/mcp.py by default. A destructive endpoint has a bigger blast radius when the caller is an LLM deciding on its own when to invoke it than when it's a human confirming a dialog. Still a normal REST endpoint either way; re-include it explicitly once you actually want that.

Auth

Build a custom auth bridge vs. fastapi_mcp's AuthConfig(dependencies=[Depends(...)])

Not wired by default (no auth in this template at all, same as fastapi_template) — but when you add it, pass your existing Depends() into AuthConfig rather than writing a separate MCP-specific auth path. fastapi_mcp's whole pitch over a generic OpenAPI→MCP converter is reusing FastAPI's own dependencies for this.

Where to build the MCP object

Inline in main.py vs. a build_mcp() function

A function (app/core/mcp.py) — lets tests/test_mcp.py inspect .tools directly without booting a live MCP session/handshake.

What was actually useful from the surveyed sources

Source

Verdict

tadata-org/fastapi_mcp (source, not just README)

The only one worth reading closely — this template's mount_http()/exclude_operations/AuthConfig usage all came from reading fastapi_mcp/server.py directly, because the README's own basic example (mcp.mount()) already calls a soft-deprecated path — worth knowing before copying it verbatim from the README.

react_mcp_server/react-mcp-server-spec.md (this repo, already existed)

Same "(a) not (b)" call, same operation_id/Field(description=...) warnings — written independently before this template, confirms the pattern rather than introducing it.

modelcontextprotocol/servers

Reference server implementations (stdio-based tool servers), not FastAPI-specific — no additional guidance for this template's actual problem (exposing an existing HTTP API), so nothing was taken from it directly.

The Medium/blog posts (Ruchi Awasthi, uselessai.in, Jayant Nehra) and mintmcp's blog

General MCP-concept explainers, largely restating what fastapi_mcp's own README already says, at a lower technical resolution. mcpservers.org is a directory listing, not a guide. None added anything beyond what's already reflected above — surveyed, not skipped out of laziness.

A live upstream bug, verified 2026-09-13

fastapi-mcp==0.4.0 (latest on PyPI) calls the mcp SDK's Server(name, description) positionally; mcp>=2.0.0 made description keyword-only, so the combination raises TypeError at import time. pyproject.toml pins mcp = "<2.0" to work around it. Re-check this pin when bumping fastapi-mcp — the fix is on the fastapi_mcp side, not something to route around with more code here.

Quick start

cp .env.example .env
poetry install
make migrate
make dev        # fastapi dev app/main.py -- REST at /v1/items, docs at /docs, MCP at /mcp
make test       # includes tests/test_mcp.py

Point an MCP client (e.g. Claude Desktop's config, or mcp-remote) at http://127.0.0.1:8000/mcp and confirm it lists create_item, get_item, list_items, and health — but not delete_item.

Extending this template

Same as fastapi_template for adding a new resource (model → schema → repository → service → route → one line in router.py) — the only addition is: give the route an explicit operation_id, and write its schema field descriptions for an LLM reader. It becomes an MCP tool automatically the next time build_mcp() runs; no separate registration step.

Change Log

Date

Change

Author

2026-09-13

Forked from fastapi_template; added fastapi_mcp wiring, explicit operation_ids, tool-facing field descriptions, and the exposure-filtering example

Ayush Sood

Contributing, security, license

See CONTRIBUTING.md, CODE_OF_CONDUCT.md, SECURITY.md. Released under the MIT License.

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