# Resend Emulator (service host)

Create an instance:
curl -s -X POST https://resend.emulators.dev/_emulate/instances
# Hosted deployments create instances lazily when the returned URL is first used. The instance URL is a capability: anyone who has it can read and modify the instance, so save the returned URLs. Never store real secrets in an emulator.
# The server generates an unguessable name. An optional {"instance":"<prefix>"} body adds a readable prefix.

Then use the returned providerBaseUrl / controlBaseUrl. Example below uses a sample instance.
# Resend Emulator

Stateful Resend emulator for email sending, domains, contacts, audiences, API keys, and an inbox UI.

Provider base URL: https://resend.your-instance.emulators.dev
Control base URL: https://resend.your-instance.emulators.dev/_emulate

Supported surfaces:
- REST API: partial at /
- Inbox UI: supported at /_inbox
- Webhooks: partial

Control endpoints:
- https://resend.your-instance.emulators.dev/_emulate/manifest
- https://resend.your-instance.emulators.dev/_emulate/coverage
- https://resend.your-instance.emulators.dev/_emulate/connections
- https://resend.your-instance.emulators.dev/_emulate/state
- https://resend.your-instance.emulators.dev/_emulate/ledger
- https://resend.your-instance.emulators.dev/_emulate/faults
- POST https://resend.your-instance.emulators.dev/_emulate/credentials
- POST https://resend.your-instance.emulators.dev/_emulate/seed
- POST https://resend.your-instance.emulators.dev/_emulate/reset

Fault injection:
Arm a one-shot provider failure with a glob pathPattern, then inspect /ledger for faulted: true.
curl -s -X POST https://resend.your-instance.emulators.dev/_emulate/faults \
  -H "content-type: application/json" \
  -d '{"match":{"method":"GET","pathPattern":"/v1/*"},"response":{"status":503,"body":{"error":"temporary"}}}'

Connect:

## Resend SDK (TypeScript)
import { Resend } from "resend";

// The Resend SDK honors RESEND_BASE_URL for the API host.
process.env.RESEND_BASE_URL = "https://resend.your-instance.emulators.dev";
const resend = new Resend("<token>");

await resend.emails.send({
  from: "onboarding@example.com",
  to: "test@example.com",
  subject: "Hello from the emulator",
  html: "<p>It works.</p>",
});

## Resend env
RESEND_BASE_URL=https://resend.your-instance.emulators.dev
RESEND_API_KEY=<token>

## curl
curl -s -X POST https://resend.your-instance.emulators.dev/emails \
  -H "authorization: Bearer <token>" \
  -H "content-type: application/json" \
  -d '{"from":"onboarding@example.com","to":"test@example.com","subject":"Hello","html":"<p>Hi</p>"}'

## Base URL (env)
RESEND_BASE_URL=https://resend.your-instance.emulators.dev

## Create a credential
curl -s -X POST https://resend.your-instance.emulators.dev/_emulate/credentials \
  -H "content-type: application/json" \
  -d '{"type":"api-key"}'

## Inspect requests
curl -s https://resend.your-instance.emulators.dev/_emulate/ledger