Resend

Lightweight, dependency-free, in-memory Resend REST API fake for testing code that uses the real resend Node.js SDK (and the language-agnostic Resend REST API).

Default port: 4651

Quick start

Start the server:

import { ResendServer } from "./services/resend/src/server.js";

const server = new ResendServer(4651);
await server.start();
// ... run your app/tests ...
await server.stop();

Point the real resend client at it. The Resend SDK reads baseUrl from the options object, so override the base URL to the fake:

import { Resend } from "resend";

const resend = new Resend("re_parlel_test_key", {
  baseUrl: "http://127.0.0.1:4651", // point at the parlel fake
});

const { data, error } = await resend.emails.send({
  from: "Acme <onboarding@resend.dev>",
  to: ["delivered@resend.dev"],
  subject: "hello world",
  html: "<p>it works!</p>",
});
// data.id => a generated UUID, error => null

Every send is captured in memory and can be inspected via the /__parlel/* endpoints (see below).

Implemented operations

All routes require a Authorization: Bearer <key> header (any non-empty bearer token is accepted, matching how a local test key behaves). State is in-memory and ephemeral.

Emails — the surface resend.emails and resend.batch call

• POST /emails — send an email (resend.emails.send). Validates the payload, captures it, returns 200 { id }.
• GET /emails/:id — retrieve a sent email (resend.emails.get). Returns the documented { object: "email", id, to, from, created_at, subject, html, text, bcc, cc, reply_to, last_event, scheduled_at, tags } shape.
• PATCH /emails/:id — update/reschedule a scheduled email (resend.emails.update). Returns 200 { object: "email", id }.
• POST /emails/:id/cancel — cancel a scheduled email (resend.emails.cancel). Returns 200 { object: "email", id }.
• POST /emails/batch — send up to 100 emails at once (resend.batch.send). Returns 200 { data: [{ id }, ...] }. attachments and scheduled_at are rejected, matching the real API limitation.

Supports Idempotency-Key header on POST /emails: a repeated key replays the original response without creating a new email.

Domains — resend.domains

• POST /domains — create a domain (201); returns DNS records (SPF MX, SPF TXT, three DKIM CNAMEs, and a Tracking CNAME), status: "not_started", region, capabilities.
• GET /domains — list domains ({ object: "list", data: [...] }).
• GET /domains/:id — retrieve a domain.
• PATCH /domains/:id — update tracking/TLS settings.
• POST /domains/:id/verify — trigger verification (status → pending).
• DELETE /domains/:id — remove a domain.

API keys — resend.apiKeys

• POST /api-keys — create a key (201); returns { id, object: "api_key", token } (the token is only shown once, matching the real API response). A seeded default key always exists.
• GET /api-keys — list keys ({ object: "list", data: [...] }).
• DELETE /api-keys/:id — remove a key.

Audiences — resend.audiences

• POST /audiences — create (201 { object: "audience", id, name }).
• GET /audiences — list.
• GET /audiences/:id — retrieve.
• DELETE /audiences/:id — remove (also clears its contacts).

Contacts — resend.contacts (nested under an audience)

• POST /audiences/:audienceId/contacts — create (201 { object: "contact", id }). Custom properties are stored and echoed back on retrieve.
• GET /audiences/:audienceId/contacts — list ({ object: "list", has_more, data: [...] }).
• GET /audiences/:audienceId/contacts/:idOrEmail — retrieve by id or email. Returns the real contact shape { object: "contact", id, email, first_name, last_name, created_at, unsubscribed, properties }.
• PATCH /audiences/:audienceId/contacts/:idOrEmail — update first/last name, unsubscribed.
• DELETE /audiences/:audienceId/contacts/:idOrEmail — remove.

Broadcasts — resend.broadcasts

• POST /broadcasts — create (201 { id }). send: true sends immediately (status: "sent"); with scheduled_at it is queued. scheduled_at without send: true is rejected.
• GET /broadcasts — list.
• GET /broadcasts/:id — retrieve.
• PATCH /broadcasts/:id — update name/subject/from/html/text.
• POST /broadcasts/:id/send — send now, or schedule with { scheduled_at }.
• DELETE /broadcasts/:id — remove (rejected if already sent).

Service & inspection operations (parlel extensions, not part of Resend)

• GET / — service metadata ({ name, version, protocol, documentation }).
• GET /health — health check ({ status: "ok" }).
• POST /__parlel/reset — reset all in-memory state.
• GET /__parlel/emails — list every captured email with the full original request preserved under _request ({ emails: [...], count }).
• GET /__parlel/emails/:id — fetch one captured email (including _request).
• DELETE /__parlel/emails — clear only the captured mailbox, leaving other state intact.
• OPTIONS * — CORS preflight (204).

Surface coverage

This emulator faithfully replicates the API surface most application code and agents exercise. Anything below the supported lines is either an intentional design choice for a fast, zero-cost local emulator (✓ By design) or a candidate for a future release (⟳ Roadmap) — never a silent inaccuracy.

Legend: ✅ fully supported · ◐ accepted (stored, not strictly enforced) · ✓ by design · ⟳ on the roadmap.

Error codes & shapes

Errors use the Resend envelope:

{ "statusCode": 422, "name": "validation_error", "message": "..." }

The generic validation_error returns 400 (matching the real API's errors reference); only the typed errors above use 422.

The official resend Node SDK does not throw on these; it resolves with { data: null, error: <envelope> }.

Manifest

See services/resend/manifest.json:

• name: resend, image: parlel/resend:1.0
• port: 4651, protocol: http, healthcheck: /health, startup ≈ 100ms
• env: RESEND_API_KEY, RESEND_BASE_URL

Configuration — test.env

Copy these into your test.env (used by the bridge sidecar flow). Tokens are Parlel's seeded test credentials — any non-empty value is accepted by the emulator, so you rarely need to change them. Swap in real credentials only when pointing at the live service in prod.env.

RESEND_API_KEY=re_parlel_test_key
RESEND_BASE_URL=http://parlel-bridge:4651