Getting Started

Local drop-in replacement for Vercel, GitHub, Google, Slack, Apple, Microsoft, Okta, AWS, Resend, Stripe, MongoDB Atlas, Clerk, Linear, and Twilio APIs. Built for CI and no-network sandboxes. Fully stateful, production-fidelity API emulation. Not mocks.

Quick Start

npx emulate

All services start with sensible defaults. No config file needed:

Vercel on http://localhost:4000
GitHub on http://localhost:4001
Google on http://localhost:4002
Slack on http://localhost:4003
Apple on http://localhost:4004
Microsoft on http://localhost:4005
Okta on http://localhost:4006
AWS on http://localhost:4007
Resend on http://localhost:4008
Stripe on http://localhost:4009
MongoDB Atlas on http://localhost:4010
Clerk on http://localhost:4011
Linear on http://localhost:4012
Twilio on http://localhost:4013

CLI

# Start all services (zero-config)
npx emulate

# Start specific services
npx emulate --service vercel,github

# Custom port
npx emulate --port 3000

# Use a seed config file
npx emulate --seed config.yaml

# Generate omitted service secrets into a private file
npx emulate start --seed config.yaml --generated-secrets-file .emulate-secrets.json

# Generate a starter config
npx emulate init

# Generate config for a specific service
npx emulate init --service github

# List available services
npx emulate list

Options

Flag	Default	Description
`-p, --port`	`4000`	Base port (auto-increments per service)
`-s, --service`	all	Comma-separated services to enable
`--seed`	auto-detect	Path to seed config (YAML or JSON)
`--base-url`	none	Override the advertised base URL (supports `{service}` template)
`--portless`	off	Serve over HTTPS through portless and register service aliases
`--generated-secrets-file`	none	Generate omitted service secrets and write them to a new owner-only JSON file

The generated-secrets destination must not exist. emulate removes inherited ACLs, verifies effective owner-only access, and publishes the complete file before startup. Handled startup failures remove the invocation-owned artifact. A hard termination can leave a complete artifact that requires manual recovery. Linux requires setfacl and getfacl from the acl package. The flag fails closed when access controls cannot be verified and is not supported on Windows.

The port can also be set via EMULATE_PORT or PORT environment variables.

Programmatic API

You can also use emulate as a library in your tests. See the Programmatic API page for createEmulator, Vitest/Jest setup, and instance methods.

Framework Integration

Embed emulators directly in your Next.js or Nuxt app so they run on the same origin. See the Next.js Integration and Nuxt Integration pages for setup instructions.

GitHub App flows expose secret-free installation-token metadata through an emulator-only inspection route. See the GitHub documentation for details.