Parlel – 250 API emulators on local Docker for coding AI agents

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250+ service emulators on local Docker — Stripe, Postgres, Slack, S3, OpenAI and more, speaking real wire protocols.

A verification layer for AI coding agents (and a "mock everything locally" tool for everyone else).

SERVICES="postgres,redis,stripe,openai,slack" docker compose up

That's it. Five real services are now listening on localhost — Postgres on 5432, Redis on 6379, Stripe on 4757, and so on. Point your app at them with unmodified real drivers and run your code. No accounts, no API keys, no cost, no side effects.

Why

Code that talks to databases, payment APIs, queues and SaaS needs testing. Today you either:

Mock everything — fast, but mocks lie and miss real bugs.

Use the real services — accurate, but slow, costs money, needs secrets, and has side effects (real charges, real emails).

Parlel is the third option: real wire protocols, in-memory, instant, free. The Postgres emulator speaks the actual Postgres protocol — psycopg/pg connect unmodified. The Stripe emulator speaks the real Stripe REST API — stripe-node works as-is. Your code is identical to production; only the endpoint changes.

This is especially useful for AI coding agents: an agent can spin up exactly the services its code touches, run it, assert, and tear down — all locally, all free, with zero risk to production.

Quick start

With Docker (recommended — collision-safe):

git clone https://github.com/dksingh1997/parlel && cd parlel npm install # one-time, for the launcher

start just what you need

SERVICES="postgres,redis,stripe" npm run up

or everything

SERVICES=all npm run up

npm run up publishes only the ports for the services you ask for, and if a port is already taken on your machine (a local Postgres on 5432, say) it remaps that one service to a free port and tells you which one:

parlel: 1 host port(s) were busy — remapped to free ports: • postgres: connect on localhost:15000 (container 5432)

Plain docker compose up also works if you'd rather — see docker-compose.yml.

With plain docker run:

docker build -t parlel . docker run -p 5432:5432 -p 4757:4757 -e SERVICES="postgres,stripe" parlel

Without Docker (pure Node, no install needed):

SERVICES="postgres,redis,stripe" node src/launch.mjs

Then use the services with your normal drivers:

import psycopg, redis, stripe

db = psycopg.connect("postgres://parlel:parlel@localhost:5432/parlel") cache = redis.Redis(host="localhost", port=6379) stripe.api_base = "http://localhost:4757" stripe.api_key = "sk_test_parlel"

import pg from "pg"; import Stripe from "stripe";

const db = new pg.Client("postgres://parlel:parlel@localhost:5432/parlel"); const stripe = new Stripe("sk_test_parlel", { host: "localhost", port: 4757, protocol: "http" });

See examples/ for a runnable end-to-end flow, and .env.example for every service's port + seeded test credentials.

What's included

250+ services across these categories:

Category Count Examples

AWS 59 S3, DynamoDB, SQS, SNS, Lambda, SES, Kinesis

Payments 20 Stripe, PayPal, Braintree, Adyen, Square, Razorpay

Dev / Source 19 GitHub, GitLab, Vercel, Sentry, CircleCI

AI 18 OpenAI, Anthropic, Cohere, Mistral, Groq

Email 15 SendGrid, Mailgun, Resend, Postmark, SES

Forms 10 Typeform, Jotform, Tally, Google Forms

Analytics 10 Mixpanel, Amplitude, PostHog, Segment

Productivity 10 Jira, Notion, Slack, Linear, Asana, Trello

Storage 10 S3, GCS, Azure Blob, Dropbox, Cloudinary

Social 10 X/Twitter, LinkedIn, Instagram, Reddit, Discord

CRM 10 Salesforce, HubSpot, Pipedrive, Freshsales

Auth 9 Auth0, Clerk, Cognito, Keycloak, Okta

Search 7 Elasticsearch, Meilisearch, Qdrant, Pinecone

Databases 6 Postgres, MySQL, MongoDB, Redis, Cassandra, Supabase

Azure / GCP / Google / Microsoft 20 Key Vault, Pub/Sub, BigQuery, Sheets, Teams

Messaging 4 Kafka, RabbitMQ, EventBridge

Marketing / SaaS / … 11 Mailchimp, Klaviyo, Shopify, Zendesk

TCP services (real wire protocols, reached with native drivers): Postgres, Redis, MySQL, MongoDB, Kafka, RabbitMQ, Cassandra. Everything else is HTTP.

Full service list

See .env.example for all 250 services with their ports and seeded credentials, and docs/ for a per-service API reference.

Real protocols, not stubs

Each emulator implements the actual wire protocol or REST contract, verified against the real client libraries. The test suite connects with pg, redis, mysql2, mongodb, kafkajs, amqplib, cassandra-driver, the AWS SDK, Stripe, and more — and asserts real round-trips.

npm install # dev deps: the real driver libraries + vitest npm test # per-service fidelity tests npm run probe # boot a set and health-check every service

Configuration

SERVICES — comma-separated slugs, or all. Defaults to postgres,redis.

Ports — each service uses its canonical port (see .env.example).

Credentials — seeded test values (e.g. sk_test_parlel); any non-empty value is accepted, so you rarely need to change them.

Control plane

Alongside the emulators, Parlel runs an additive admin server on localhost:4700. Open it in a browser for a live dashboard — every running service, its connection string, the request log, a state inspector, and reset buttons, auto-refreshing every 2 seconds.

You can also drive it programmatically. List what's running, inspect state, and — most usefully — reset every service to a clean slate between tests without restarting anything:

beforeEach(() => fetch("http://127.0.0.1:4700/reset", { method: "POST" }));

GET /services returns each service's port and a ready-to-use connection string. You can also inspect the request log (GET /services/:slug/requests — "did my code call the API the way I think it did?") and preload fixtures (POST /services/:slug/seed, or a parlel.fixtures.json loaded on boot). See docs/control-plane.md. Disable with PARLEL_CONTROL=0.

How it works

your app / agent ──▶ localhost: ──▶ in-memory emulator (real protocol) (unchanged) (no bridge, no proxy) (ephemeral, zero side effects)

Each emulator is dependency-free Node holding state in memory. State is ephemeral — restart for a clean slate. No data ever leaves your machine.

Everything runs locally, so the official client libraries connect directly — psycopg/pg to localhost:5432, kafkajs to localhost:9092, redis to localhost:6379, and so on. There is no proxy, no bridge, and no shim: the TCP services (Postgres, MySQL, MongoDB, Kafka, RabbitMQ, Cassandra, Redis) speak their real wire protocols straight to the port. (Kafka advertises localhost:9092 in its metadata, so kafkajs reconnects land on the emulator.)

Add a service

Adding an emulator is a manifest + a server.js + a test. See CONTRIBUTING.md — it takes about five minutes.

Roadmap

MCP server so agents can drive services by tool call.

Record / replay against real upstreams.

More services (open an issue to request one).

License

MIT.

About

A verification layer for AI coding agents. 250+ real-protocol service emulators (Stripe, Postgres, Slack, S3, OpenAI…) on local Docker.

parlel.com

Topics

testing

emulator

docker

integration-testing

mocking

api-mock

ai-agents

localstack-alternative

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License

MIT license

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