mcp-mongo-server

MCP MongoDB Server

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A Model Context Protocol (MCP) server that lets AI assistants work with your MongoDB databases. It exposes your collections, infers their schemas, and runs queries, aggregations, and writes through a standard interface — so tools like Claude Desktop and Cursor can read and reason about your data.

Demo


Why use it

• Talk to your database in plain language — the assistant discovers your collections and their shape automatically.
• Safe by default — turn on read-only mode to let an assistant explore without any risk of changing data.
• Works everywhere — connects to standalone, replica set, sharded, and Atlas deployments, over plain or TLS connections.

Key Features

• Read-Only Mode — blocks every write path (insert, update, index creation, and aggregation stages like $out/$merge that could modify data).
• Smart ObjectId Handling — configurable auto/none/force conversion of 24-character hex strings to ObjectIds.
• Schema Inference — automatic collection schema detection from document samples.
• Query & Aggregation — full query and aggregation pipeline support, with optional explain plans.
• Write Operations — insert, update, and index creation (when read-only mode is off).
• Time Conversion — a convertTime helper turns Unix timestamps and date strings into UTC/GMT/ISO, so date queries stay unambiguous across timezones.
• Progress & Cancellation — long operations report progress and can be cancelled mid-flight.
• Two Transports — run locally over stdio, or expose an HTTP endpoint for remote access.

Requirements

• Node.js 20 or newer

Quick Start

Point the server at your database — no install step needed:

npx -y mcp-mongo-server mongodb://localhost:27017/mydatabase

Explore safely, without any chance of changing data:

npx -y mcp-mongo-server mongodb://localhost:27017/mydatabase --read-only

Usage

Local (stdio)

This is the default, used by Claude Desktop, Cursor, and other local clients:

npx -y mcp-mongo-server "mongodb://user:pass@localhost:27017/mydatabase"

Remote (HTTP)

Expose an HTTP endpoint at /mcp for remote or multi-client access:

npx -y mcp-mongo-server "mongodb://user:pass@localhost:27017/mydatabase" --transport http --port 3001

By default, only requests without a browser Origin (CLIs, IDEs) and requests from localhost are accepted; everything else is rejected with 403 to guard against DNS-rebinding attacks. Allow specific browser origins with --allowed-origins:

npx -y mcp-mongo-server "mongodb://..." --transport http --port 3001 --allowed-origins "https://app.example.com"

Options

| Flag | Description | |------|-------------| | --read-only, -r | Block all write operations | | --allow-cross-db | Allow aggregation $out/$merge/$lookup to target other databases (off by default) | | --allow-server-js | Allow server-side JavaScript operators $function/$where/$accumulator (off by default) | | --transport, -t | stdio (default) or http | | --port, -p | HTTP port (default 3001) | | --allowed-origins | Comma-separated browser origins to allow in HTTP mode | | --json-limit | Max HTTP request body size (default 10mb) | | --auth-token | Require Authorization: Bearer <token> on the HTTP endpoint |

Environment Variables

| Variable | Description | |----------|-------------| | MCP_MONGODB_URI | MongoDB connection URI (alternative to the argument) | | MCP_MONGODB_READONLY | Enable read-only mode ("true") | | MCP_MONGODB_ALLOW_CROSS_DB | Allow cross-database aggregation stages ("true") | | MCP_MONGODB_ALLOW_SERVER_JS | Allow server-side JavaScript operators ("true") | | MCP_PORT | HTTP port | | MCP_HTTP_ALLOWED_ORIGINS | Comma-separated browser origins to allow in HTTP mode | | MCP_HTTP_JSON_LIMIT | Max HTTP request body size (default 10mb) | | MCP_HTTP_AUTH_TOKEN | Bearer token required to access the HTTP endpoint |

Security

Database scope. The server operates on the database in your connection string. Aggregation stages that reach another database ($out, $merge, $lookup with an explicit db) are rejected by default, so a pipeline can't quietly read from or write to databases you didn't point it at. Enable them with --allow-cross-db if you need them.

Server-side JavaScript. The aggregation operators $function, $where, and $accumulator run arbitrary JavaScript on the MongoDB server. They are rejected by default; enable them with --allow-server-js if you trust the pipelines being run.

Read-only mode blocks every write path, including aggregation stages that write or run server-side JavaScript ($out, $merge, $function, $where, $accumulator).

Least privilege. Application-level checks only go so far — the strongest guarantee comes from the database. Connect with a MongoDB user scoped to just the database you need, with read-only permissions when the assistant only needs to explore. That way the database itself enforces the boundary, as defense in depth.

Documentation

• Integration Guide — Claude Desktop, Windsurf, Cursor, Docker
• Available Tools — query, aggregate, update, insert, and more
• Development — setup, scripts, and debugging
• Contributing

License

MIT — see LICENSE for details.