resend

Original：🇺🇸 English

Translated

Emulated Resend email API for local development and testing. Use when the user needs to send emails locally, test transactional email flows, implement magic link or verification code auth, inspect sent emails, manage domains/contacts/API keys, or work with the Resend API without sending real emails. Triggers include "Resend API", "emulate Resend", "send email locally", "test email", "magic link", "verification email", "email inbox", "RESEND_BASE_URL", or any task requiring a local email API.

16installs

Sourcevercel-labs/emulate

Added on2026-04-08

NPX Install

npx skill4agent add vercel-labs/emulate resend

SKILL.md Content

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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. Every call to

POST /emails

stores the message locally so you can inspect it programmatically or in the browser.

Start

bash

# Resend only
npx emulate --service resend

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

Or programmatically:

typescript

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.

bash

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:

bash

RESEND_BASE_URL=http://localhost:4000

typescript

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: 'hello@example.com',
  to: 'user@example.com',
  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

typescript

// next.config.ts
import { withEmulate } from '@emulators/adapter-next'

export default withEmulate({
  env: {
    RESEND_BASE_URL: `http://localhost:${process.env.PORT ?? '3000'}/emulate/resend`,
  },
})

typescript

// app/emulate/[...path]/route.ts
import { createEmulateHandler } from '@emulators/adapter-next'
import * as resend from '@emulators/resend'

export const { GET, POST, PUT, PATCH, DELETE } = createEmulateHandler({
  services: {
    resend: {
      emulator: resend,
      seed: {
        domains: [{ name: 'example.com' }],
      },
    },
  },
})

Direct fetch

If you cannot use the SDK or env var, call the emulator directly:

typescript

await fetch('http://localhost:4000/emails', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
    'Authorization': 'Bearer re_test_key',
  },
  body: JSON.stringify({
    from: 'hello@example.com',
    to: 'user@example.com',
    subject: 'Hello',
    html: '<p>It works!</p>',
  }),
})

Seed Config

yaml

resend:
  domains:
    - name: example.com
      region: us-east-1
  contacts:
    - email: test@example.com
      first_name: Test
      last_name: User
      audience: Default

Retrieving Sent Emails

This is the key differentiator of the emulator: every email sent via

POST /emails

is stored and queryable.

Inbox UI

Browse sent emails in the browser:

http://localhost:4000/inbox

REST API

bash

# List all sent emails
curl http://localhost:4000/emails \
  -H "Authorization: Bearer re_test_key"

# Get a single email by ID
curl http://localhost:4000/emails/<id> \
  -H "Authorization: Bearer re_test_key"

Extracting Data from Emails (tests, agents)

Useful for completing magic link, verification code, or password reset flows programmatically:

bash

# Get the latest email ID
EMAIL_ID=$(curl -s http://localhost:4000/emails \
  -H "Authorization: Bearer re_test_key" | jq -r '.data[0].id')

# Extract a 6-digit code from the HTML body
CODE=$(curl -s http://localhost:4000/emails/$EMAIL_ID \
  -H "Authorization: Bearer re_test_key" | jq -r '.html' | grep -oE '[0-9]{6}')

echo "Verification code: $CODE"

API Endpoints

Emails

bash

# Send an email
curl -X POST http://localhost:4000/emails \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"from": "hello@example.com", "to": "user@example.com", "subject": "Hello", "html": "<p>Hi</p>"}'

# Send batch (up to 100)
curl -X POST http://localhost:4000/emails/batch \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '[{"from": "a@example.com", "to": "b@example.com", "subject": "One", "html": "<p>1</p>"}]'

# List all emails
curl http://localhost:4000/emails \
  -H "Authorization: Bearer $TOKEN"

# Get email by ID
curl http://localhost:4000/emails/<id> \
  -H "Authorization: Bearer $TOKEN"

# Cancel a scheduled email
curl -X POST http://localhost:4000/emails/<id>/cancel \
  -H "Authorization: Bearer $TOKEN"

Supported fields:

from

to

subject

html

text

cc

bcc

reply_to

headers

tags

scheduled_at

Domains

bash

# Create domain
curl -X POST http://localhost:4000/domains \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"name": "example.com", "region": "us-east-1"}'

# List domains
curl http://localhost:4000/domains \
  -H "Authorization: Bearer $TOKEN"

# Get domain
curl http://localhost:4000/domains/<id> \
  -H "Authorization: Bearer $TOKEN"

# Verify domain (instantly marks all records as verified)
curl -X POST http://localhost:4000/domains/<id>/verify \
  -H "Authorization: Bearer $TOKEN"

# Delete domain
curl -X DELETE http://localhost:4000/domains/<id> \
  -H "Authorization: Bearer $TOKEN"

API Keys

bash

# Create API key
curl -X POST http://localhost:4000/api-keys \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"name": "Production"}'

# List API keys
curl http://localhost:4000/api-keys \
  -H "Authorization: Bearer $TOKEN"

# Delete API key
curl -X DELETE http://localhost:4000/api-keys/<id> \
  -H "Authorization: Bearer $TOKEN"

Audiences

bash

# Create audience
curl -X POST http://localhost:4000/audiences \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"name": "Newsletter"}'

# List audiences
curl http://localhost:4000/audiences \
  -H "Authorization: Bearer $TOKEN"

# Delete audience
curl -X DELETE http://localhost:4000/audiences/<id> \
  -H "Authorization: Bearer $TOKEN"

Contacts

bash

# Create contact in an audience
curl -X POST http://localhost:4000/audiences/<audience_id>/contacts \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"email": "user@example.com", "first_name": "Jane", "last_name": "Doe"}'

# List contacts in an audience
curl http://localhost:4000/audiences/<audience_id>/contacts \
  -H "Authorization: Bearer $TOKEN"

# Delete contact
curl -X DELETE http://localhost:4000/audiences/<audience_id>/contacts/<id> \
  -H "Authorization: Bearer $TOKEN"

Webhooks

The emulator dispatches webhook events when state changes:

```
email.sent
```
and
```
email.delivered
```
on
```
POST /emails
```
```
domain.created
```
and
```
domain.deleted
```
on domain operations
```
contact.created
```
and
```
contact.deleted
```
on contact operations

Common Patterns

Magic Link / Verification Code Flow

bash

TOKEN="re_test_key"
BASE="http://localhost:4000"

# 1. Send verification email
curl -X POST $BASE/emails \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"from": "auth@example.com", "to": "user@example.com", "subject": "Your code", "html": "<p>Code: <strong>482910</strong></p>"}'

# 2. Retrieve the email
EMAIL_ID=$(curl -s $BASE/emails -H "Authorization: Bearer $TOKEN" | jq -r '.data[0].id')

# 3. Read the HTML body
curl -s $BASE/emails/$EMAIL_ID -H "Authorization: Bearer $TOKEN" | jq -r '.html'

Send and Verify in a Test

typescript

import { createEmulator } from 'emulate'
import { Resend } from 'resend'

const emu = await createEmulator({ service: 'resend', port: 4000 })

process.env.RESEND_BASE_URL = emu.url
const resend = new Resend('re_test_key')

// Send
await resend.emails.send({
  from: 'auth@example.com',
  to: 'user@test.com',
  subject: 'Verify',
  html: '<p>Code: <strong>123456</strong></p>',
})

// Retrieve
const res = await fetch(`${emu.url}/emails`, {
  headers: { Authorization: 'Bearer re_test_key' },
})
const { data: emails } = await res.json()
console.log(emails[0].html) // contains "123456"

resend

NPX Install

Tags

SKILL.md Content

Resend Email API Emulator

Start

Auth

Pointing Your App at the Emulator

Environment Variable (Resend SDK)

Embedded in Next.js (adapter-next)

Direct fetch

Seed Config

Retrieving Sent Emails

Inbox UI

REST API

Extracting Data from Emails (tests, agents)

API Endpoints

Emails

Domains

API Keys

Audiences

Contacts

Webhooks

Common Patterns

Magic Link / Verification Code Flow

Send and Verify in a Test