resend

Resend Email API Emulator

Fully stateful Resend API emulation. Emails, domains, API keys, audiences, and contacts persist in memory. Sent emails are captured and viewable through the inbox UI or the REST API.

No real emails are sent. Accepted calls to POST /emails store the message locally so you can inspect it programmatically or in the browser. Validated sends also record attempts, including recipient rejections.

Start

Local listeners bind to 127.0.0.1 by default. For access from containers or other machines, pass --host 0.0.0.0 to the CLI or hostname: '0.0.0.0' to createEmulator. Configure --base-url or baseUrl for advertised URLs reachable by those clients.

# Resend only
npx emulate --service resend

# Default port (when run alone)
# http://localhost:4000

Or programmatically:

import { createEmulator } from 'emulate'

const resend = await createEmulator({ service: 'resend', port: 4000 })
// resend.url === 'http://localhost:4000'

Auth

Pass tokens as Authorization: Bearer <token>. Any re_ prefixed token is accepted.

curl http://localhost:4000/emails \
  -H "Authorization: Bearer re_test_key"

When no token is provided, requests fall back to the default user.

Pointing Your App at the Emulator

Environment Variable (Resend SDK)

The official Resend Node.js SDK reads RESEND_BASE_URL at module load time. Set it to the emulator URL and the SDK works without any code changes:

RESEND_BASE_URL=http://localhost:4000

import { Resend } from 'resend'

// No baseUrl argument needed; the SDK reads RESEND_BASE_URL automatically.
const resend = new Resend('re_test_key')

await resend.emails.send({
  from: '[email protected]',
  to: '[email protected]',
  subject: 'Hello',
  html: '<p>It works!</p>',
})

Embedded in Next.js (adapter-next)

When using @emulators/adapter-next, the emulator runs inside your Next.js app at /emulate/resend. Set RESEND_BASE_URL via next.config.ts: