Emulators: LocalDB Simulator

Redis Emulator Ready

The Redis emulator implements the full RESP (REdis Serialization Protocol) over TCP. It is wire-compatible with ioredis, redis (node-redis), and any other RESP client.

Connection

// ioredis
import Redis from 'ioredis';
const redis = new Redis('redis://127.0.0.1:6379');

// With password
const redis = new Redis('redis://:mypassword@127.0.0.1:6379');

// node-redis
import { createClient } from 'redis';
const client = createClient({ url: 'redis://127.0.0.1:6379' });
await client.connect();

Supported commands

Category	Commands
Strings	`GET SET DEL EXISTS MGET MSET INCR DECR INCRBY DECRBY INCRBYFLOAT APPEND STRLEN GETSET SETNX SETEX PSETEX GETEX GETDEL SETRANGE GETRANGE`
Hashes	`HGET HSET HDEL HEXISTS HGETALL HKEYS HVALS HLEN HMGET HMSET HINCRBY HINCRBYFLOAT HSETNX`
Lists	`LPUSH LPUSHX RPUSH RPUSHX LPOP RPOP LLEN LRANGE LINDEX LSET LINSERT LREM LTRIM`
Sets	`SADD SREM SISMEMBER SMISMEMBER SMEMBERS SCARD SUNION SINTER SDIFF SUNIONSTORE SINTERSTORE SDIFFSTORE SRANDMEMBER SPOP SMOVE`
Sorted Sets	`ZADD ZREM ZSCORE ZCARD ZRANK ZREVRANK ZINCRBY ZRANGE ZREVRANGE ZRANGEBYSCORE ZREVRANGEBYSCORE ZCOUNT ZPOPMIN ZPOPMAX ZRANDMEMBER ZUNIONSTORE ZINTERSTORE`
TTL	`EXPIRE PEXPIRE EXPIREAT PEXPIREAT TTL PTTL PERSIST`
Pub/Sub	`SUBSCRIBE UNSUBSCRIBE PUBLISH`
Server	`PING ECHO SELECT DBSIZE FLUSHDB FLUSHALL KEYS SCAN RANDOMKEY INFO OBJECT (ENCODING/REFCOUNT) TYPE RENAME RENAMENX WAIT`

Persistence

Enable persistence in config to snapshot data to LevelDB every 5 seconds:

redis:
  persistence: true
  data_dir: ./.localdb/redis

Note: SELECT (multiple databases 0–15) is supported. The data browser shows keys for a selected DB index.

PostgreSQL Emulator Ready

Powered by pglite: a WebAssembly build of real PostgreSQL 16 embedded in Node.js. Clients connect via the standard PostgreSQL wire protocol; no special drivers needed.

Connection

// node-postgres (pg)
import { Pool } from 'pg';
const pool = new Pool({
  host: '127.0.0.1',
  port: 5432,
  database: 'myapp_dev',
  user: 'postgres',
});

// With connection string
const pool = new Pool({
  connectionString: 'postgresql://postgres@127.0.0.1:5432/myapp_dev'
});

// Prisma: datasource in schema.prisma
// datasource db {
//   provider = "postgresql"
//   url      = env("DATABASE_URL")
// }
// DATABASE_URL=postgresql://postgres@127.0.0.1:5432/myapp_dev

Multi-database support

Define multiple databases in config. Each database is a separate pglite instance:

postgres:
  enabled: true
  databases:
    - myapp_dev
    - myapp_test    # isolated DB for tests
    - analytics

Authentication

Config	Auth method	Connection
`password: ""`	Trust (no password)	`postgresql://postgres@127.0.0.1:5432/db`
`password: "secret"`	MD5	`postgresql://postgres:secret@127.0.0.1:5432/db`

Supported features

✓ DDL: CREATE/DROP TABLE, INDEX, SCHEMA, SEQUENCE
✓ DML: SELECT, INSERT, UPDATE, DELETE with WHERE, JOIN, GROUP BY, ORDER BY
✓ Transactions: BEGIN / COMMIT / ROLLBACK
✓ Extended query protocol (prepared statements, parameterised queries)
✓ Data types: JSONB, BOOLEAN, TIMESTAMPTZ, UUID, ARRAY, NUMERIC
✓ Functions, aggregates, CTEs, window functions

pglite: ~95% of standard PostgreSQL SQL is supported. Complex features like logical replication, extensions (PostGIS, pgvector), and foreign data wrappers are not available.

MongoDB Emulator Ready

Powered by mongodb-memory-server, which downloads the official mongod binary for your platform on first run (~77 MB, cached in ~/.cache/mongodb-binaries). 100% wire-compatible: use the standard mongodb driver without modification.

First-run binary download: When MongoDB first starts, mongodb-memory-server downloads the official mongod binary for your OS (~77 MB). This happens once and is cached. Subsequent starts are instant (~100 ms). Set MONGOMS_DOWNLOAD_DIR to a shared path to reuse across projects.

Connecting

// Official mongodb driver (Node.js)
import { MongoClient } from 'mongodb';

const client = new MongoClient('mongodb://127.0.0.1:27017');
await client.connect();
const db = client.db('myapp_dev');

// Mongoose
await mongoose.connect('mongodb://127.0.0.1:27017/myapp_dev');

# .env
MONGODB_URI=mongodb://127.0.0.1:27017/myapp_dev

Configuration

mongodb:
  enabled: true
  port: 27017
  persistence: false        # true → WiredTiger engine, data survives restart
  data_dir: ./.localdb/mongodb  # required when persistence: true
  databases:
    - myapp_dev
    - myapp_test

Field	Type	Default	Description
`enabled`	boolean	`true`	Enable / disable the emulator.
`port`	number	`27017`	TCP port to bind on `127.0.0.1`.
`persistence`	boolean	`false`	If `true`, uses WiredTiger engine with `data_dir` for durable storage.
`data_dir`	string	n/a	Directory for persistent data. Required when `persistence: true`.
`databases`	string[]	`["test"]`	Logical database names exposed in the data browser. The wire protocol allows any database name regardless of this list.

Supported features

✓ Full CRUD: insertOne/Many, findOne/find, updateOne/Many, deleteOne/Many, replaceOne
✓ Aggregation pipeline ($match, $group, $sort, $project, $lookup, …)
✓ Indexes: createIndex, unique indexes, compound indexes
✓ Multi-database: data is fully isolated between databases
✓ Persistence: WiredTiger storage engine, data survives restarts
✓ Mongoose, Prisma, and any driver that targets the MongoDB wire protocol

Tip: The emulator is an unmodified mongod binary, so compatibility is effectively 100% for MongoDB 8.x features.