JSON DB MCP Server (FastAPI + FastMCP)

A minimal Model Context Protocol (MCP) server that also exposes a small REST API.
Data is stored in a single JSON file (db.json) as collections of items with auto-generated UUIDs.

• MCP Tools: db.add_item, db.get_item, db.list_items, db.update_item, db.delete_item

• REST Endpoints: POST/GET/PUT/DELETE /db/{collection}[/{id}]

• Transports: HTTP (recommended) and SSE (optional)

• Stack: Python, FastAPI, Uvicorn, FastMCP

Features

• Simple JSON-file database with atomic writes

• Thread-safe in a single-process server using a lock

• Shared core logic for both MCP tools and REST

• Works with VS Code Copilot (Chat) and Gemini CLI as an MCP server

Related MCP server: MongoDB MCP Server

Requirements

• Python 3.10+

• uv (recommended) or pip

• Git (optional, for version control)

Project Layout

.
├─ main.py
├─ db.json                # created on first write
└─ README.md

Installation

Using uv (recommended)

uv venv
uv pip install fastapi uvicorn fastmcp

Using pip

python -m venv .venv
source .venv/bin/activate
pip install fastapi uvicorn fastmcp

Running

Development (auto-reload)

uv run main.py
# or
uv run python main.py
# Server: http://localhost:8000

Default MCP transport: HTTP at /mcp/ (recommended).
If you prefer SSE, see MCP over SSE (optional) below.

REST API

All endpoints operate on a collection (created on first write) with items of shape:

{
  "id": "uuid-string",
  "...": "fields you provide"
}

Create

curl -X POST http://localhost:8000/db/users \
  -H "Content-Type: application/json" \
  -d '{"name":"Omar","role":"admin"}'

List

curl http://localhost:8000/db/users

Get by ID

curl http://localhost:8000/db/users/<ITEM_ID>

Update

curl -X PUT http://localhost:8000/db/users/<ITEM_ID> \
  -H "Content-Type: application/json" \
  -d '{"role":"owner"}'

Delete

curl -X DELETE http://localhost:8000/db/users/<ITEM_ID>

MCP Server (HTTP transport, recommended)

This server mounts FastMCP’s HTTP transport at /mcp/.

VS Code — GitHub Copilot (Chat)

1. Open Copilot Chat → Tools (or Add MCP).

2. Transport: HTTP

3. URL: http://localhost:8000/mcp/ (include the trailing slash)

4. Enable the server. You should see tools:

   • db.add_item, db.get_item, db.list_items, db.update_item, db.delete_item

Using tools in chat:
Select a tool from the list or ask:

Use db.add_item with collection="users" and payload={"name":"Omar"}.

Gemini CLI

Add the server via CLI (writes settings for you):

# Project-scoped (./.gemini/settings.json)
gemini mcp add --transport http jsondb http://localhost:8000/mcp/

# Or user-scoped (~/.gemini/settings.json)
gemini mcp add --scope user --transport http jsondb http://localhost:8000/mcp/

List tools:

gemini mcp list

Call a tool:

gemini mcp call jsondb db.add_item \
  --args collection=users \
  --args payload='{"name":"Omar"}'

MCP over SSE (optional)

If you prefer SSE, change the mount in main.py:

# replace the HTTP mount:
# mcp_http_app = mcp.http_app(path="/")
# app.mount("/mcp", mcp_http_app)

mcp_sse_app = mcp.sse_app()
app.mount("/mcp", mcp_sse_app)  # SSE lives under /mcp/sse/

• SSE endpoint: http://localhost:8000/mcp/sse/ (note trailing slash)

• Copilot: Transport = SSE, URL = http://localhost:8000/mcp/sse/

• Gemini CLI:

  gemini mcp add --scope user --transport sse jsondb http://localhost:8000/mcp/sse/

Many HTTP clients require a trailing slash for SSE endpoints; use /mcp/sse/.

Health Check (optional)

Add this to main.py (after app = FastAPI(...)) if you want a friendly root:

@app.get("/")
def health():
    return {"ok": True, "rest": "/db/{collection}", "mcp": "/mcp/"}

Persistence & Backups

• Data file: db.json (created on first write).

• Writes are atomic: a db.json.tmp is written then replaced.

• For safety, consider periodic snapshots (e.g., cp db.json db.json.bak in a cron job).

Authentication (optional)

For local development MCP/REST are open.
If you need auth, simplest is an API key header via FastAPI middleware and headers in your MCP client configuration. Example:

from fastapi import Request
from fastapi.responses import JSONResponse
import os

API_KEY = os.getenv("API_KEY", "")

@app.middleware("http")
async def api_key_guard(request: Request, call_next):
    if API_KEY and request.headers.get("x-api-key") != API_KEY:
        return JSONResponse(status_code=401, content={"detail": "Unauthorized"})
    return await call_next(request)

• Copilot/Gemini: configure an x-api-key header in the MCP server settings.

Troubleshooting

• 404 on /
  Expected. Use REST under /db/... and MCP at /mcp/ (HTTP) or /mcp/sse/ (SSE).

• 307 redirect from /mcp → /mcp/
  Some SSE clients don’t follow redirects. Use the trailing slash or disable redirect slashes:

  app.router.redirect_slashes = False

• SSE returns 404
  Make sure you’re hitting /mcp/sse/ (not /mcp/).

• Concurrency
  Run as a single process for file-backed DB. Multi-process/worker deployments need a real DB or OS-level file locks.

• Git push errors (VS Code AskPass socket)
  Unset helper vars or use GitHub CLI / SSH keys:

  unset GIT_ASKPASS SSH_ASKPASS VSCODE_GIT_ASKPASS_NODE VSCODE_GIT_ASKPASS_MAIN

License

Copyright© - Omar SOLIMAN