MongoDB

Lightweight, dependency-free MongoDB implementation speaking the real wire protocol (OP_MSG + BSON), so the official mongodb driver connects with zero config.

Default Connection

mongodb://parlel-bridge:27017

No auth required. Default database: parlel.

Supported Commands

Handshake / connection

hello, ismaster, ping, buildInfo, hostInfo, getParameter, whatsmyuri, connectionStatus, saslStart/saslContinue (accepted), logout, getLog, endSessions, refreshSessions.

Write

Read

Collections / databases / indexes

create, drop, dropDatabase, listCollections, listDatabases, listIndexes, createIndexes, dropIndexes, renameCollection, collStats, dbStats, validate.

Usage

Add the parlel/bridge sidecar to your test compose file. It exposes MongoDB at parlel-bridge:27017 and your app connects with the unmodified official mongodb driver — no Parlel code in the app.

include:
  - path: parlel-bridge.yml          # image: parlel/bridge
services:
  app:
    build: .
    env_file: test.env
    depends_on:
      parlel-bridge: { condition: service_healthy }

PARLEL_API_KEY=pk_... docker compose -f docker-compose.test.yml up

Then connect with the real driver against the parlel-bridge hostname:

import { MongoClient } from "mongodb";

const client = new MongoClient("mongodb://parlel-bridge:27017");
await client.connect();
const db = client.db("parlel");

await db.collection("users").insertMany([{ name: "Ada" }, { name: "Bob" }]);
const users = await db.collection("users").find({}).toArray();
await db.collection("users").updateOne({ name: "Ada" }, { $set: { role: "admin" } });

Access via MCP (Parlel Sandbox)

When MongoDB runs inside a Parlel sandbox, drive it through the sandbox's MCP endpoint with parlel_execute. The command is a JSON string — either a raw Mongo command document or wrapped with an explicit db:

Insert:

{
  "jsonrpc": "2.0", "id": 1, "method": "tools/call",
  "params": {
    "name": "parlel_execute",
    "arguments": {
      "service": "mongodb",
      "command": "{\"db\":\"parlel\",\"command\":{\"insert\":\"users\",\"documents\":[{\"name\":\"Ada\"},{\"name\":\"Bob\"}]}}"
    }
  }
}

Find:

{ "service": "mongodb", "command": "{\"db\":\"parlel\",\"command\":{\"find\":\"users\",\"filter\":{}}}" }

ObjectId values are rendered as hex strings and Date values as ISO strings in the JSON result.

Error codes & shapes

Errors use the real MongoDB envelope so driver/ODM error handling works unmodified.

Command-level errors return { ok: 0, errmsg, code, codeName }:

{ "ok": 0, "errmsg": "no such command: 'totallyBogusCommand'", "code": 59, "codeName": "CommandNotFound" }

Codes emitted match the real server (code ↔ codeName):

Write commands (insert, update, delete) return { ok: 1, n, ... } even when individual documents fail; per-document failures appear in writeErrors. A duplicate-key (E11000) write error matches MongoDB 4.2+ and includes keyPattern and keyValue (which Mongoose surfaces as err.keyPattern / err.keyValue):

{
  "ok": 1, "n": 0,
  "writeErrors": [
    {
      "index": 0,
      "code": 11000,
      "keyPattern": { "_id": 1 },
      "keyValue": { "_id": 1 },
      "errmsg": "E11000 duplicate key error collection: parlel.users index: _id_ dup key: { _id: 1 }"
    }
  ]
}

Access via Parlel Sandbox

The parlel/bridge sidecar exposes this service at parlel-bridge:27017, tunneling the raw wire protocol as TCP over the sandbox HTTPS preview proxy via WebSocket. The MongoDB driver connects to mongodb://parlel-bridge:27017 unmodified — with just an API key (or localhost if you run the bridge outside Docker and publish ports). No SSH tunnel, no daytona CLI.

Surface coverage

This emulator faithfully replicates the API surface most application code and agents exercise. Anything below the supported lines is either an intentional design choice for a fast, zero-cost local emulator (✓ By design) or a candidate for a future release (⟳ Roadmap) — never a silent inaccuracy.

Legend: ✅ fully supported · ◐ accepted (stored, not strictly enforced) · ✓ by design · ⟳ on the roadmap.

Configuration — test.env

Copy these into your test.env (used by the bridge sidecar flow). Tokens are Parlel's seeded test credentials — any non-empty value is accepted by the emulator, so you rarely need to change them. Swap in real credentials only when pointing at the live service in prod.env.

MONGO_INITDB_ROOT_USERNAME=parlel
MONGO_INITDB_ROOT_PASSWORD=parlel
MONGO_INITDB_DATABASE=parlel