resend

## Setup

1. Create an API key: https://resend.com/api-keys
2. Put it in `.env.local` (never commit it, never use `NEXT_PUBLIC_`):

```bash
RESEND_API_KEY=re_xxxxxxxx
EMAIL_FROM="Acme <onboarding@resend.dev>"
```

`new Resend()` reads `RESEND_API_KEY` automatically. You can also pass the key: `new Resend(process.env.RESEND_API_KEY)`.

> `onboarding@resend.dev` only delivers to the email address of your Resend account. To send to anyone else, verify a domain at https://resend.com/domains and use an address on it.

## Next.js (App Router)

```bash
npm install resend server-only
```

`src/lib/email.ts`:

```ts
import 'server-only';
import { Resend } from 'resend';

export async function sendWelcome(to: string, name: string) {
  const resend = new Resend(); // create inside the function so `next build` does not need the key
  const { data, error } = await resend.emails.send({
    from: process.env.EMAIL_FROM ?? 'Acme <onboarding@resend.dev>',
    to,
    subject: `Welcome, ${name}`,
    html: `<p>Hi ${name}, thanks for signing up.</p>`,
  });
  if (error) throw new Error(`${error.name}: ${error.message}`);
  return data.id;
}
```

Call `sendWelcome` from a Server Action (`'use server'`) or a Route Handler (`app/api/.../route.ts`). Do not call it from a Client Component.

`emails.send` does not throw on API errors. It returns `{ data, error }`, so always check `error`.

# Resend (npm: resend) — agent instructions

Use the official SDK for transactional email. Do not hand-roll `fetch` to api.resend.com: the SDK gives typed `{ data, error }`, React rendering and request options (`signal`, `headers`, idempotency).

## Install

```bash
npm install resend server-only
```

## Env vars

- `RESEND_API_KEY` — required. Create at https://resend.com/api-keys. `new Resend()` reads it automatically.
- `EMAIL_FROM` — e.g. `Acme <onboarding@resend.dev>`. The test sender only delivers to the Resend account owner's address. For other recipients, verify a domain at https://resend.com/domains.
- Add `.env.example` with both names. If `.gitignore` has `.env*`, add `!.env.example`.

## Next.js App Router (the one path)

```ts
// src/lib/email.ts
import 'server-only';
import { Resend } from 'resend';

export async function sendEmail(opts: { to: string; subject: string; html?: string; react?: React.ReactElement }) {
  const resend = new Resend();
  const { data, error } = await resend.emails.send({
    from: process.env.EMAIL_FROM ?? 'Acme <onboarding@resend.dev>',
    ...opts,
  });
  if (error) throw new Error(error.message);
  return data.id;
}
```

Call it from a Server Action or `app/api/*/route.ts` only.

## Three mistakes agents make

1. Instantiating `new Resend()` at module top level or in a Client Component. Create it inside a server-only function, never expose the key via `NEXT_PUBLIC_`.
2. Not checking `error`. `emails.send` returns `{ data, error }` and does not throw.
3. Using an unverified `from` address (e.g. `you@example.com`). Use `onboarding@resend.dev` for testing or a verified domain.

## Verify

- `npm run build` must pass without `RESEND_API_KEY` set.
- With no key, verify by mocking `globalThis.fetch` and asserting a POST to `https://api.resend.com/emails` with a Bearer header and the expected body.
- With a key, send to `delivered@resend.dev` and expect `data.id`.
- Do not claim a real send succeeded unless you saw a returned `id`.

{
  "description": "Official Resend SDK for Node.js: send transactional email (HTML, text or React templates) from Next.js, Express, Remix and more",
  "keywords": ["resend", "email", "transactional-email", "send-email", "email-api", "smtp-alternative", "react-email", "nextjs", "server-actions", "sdk"],
  "homepage": "https://resend.com/docs/send-with-nodejs"
}

# Resend

> Email API for developers. The `resend` npm package is the official Node.js SDK: `new Resend()` reads `RESEND_API_KEY`, `resend.emails.send({ from, to, subject, html | text | react })` returns `{ data, error }` and does not throw on API errors.

## Quickstarts

- [Send with Next.js](https://resend.com/docs/send-with-nextjs.md): App Router, Server Actions and Route Handlers
- [Send with Node.js](https://resend.com/docs/send-with-nodejs.md): install, API key, first email

## API reference

- [Send email](https://resend.com/docs/api-reference/emails/send-email.md): request fields, responses, errors
- [Idempotency keys](https://resend.com/docs/dashboard/emails/idempotency-keys.md): safe retries

## Setup

- [Verify a domain](https://resend.com/docs/dashboard/domains/introduction.md): required to send to anyone except your own account address
- [API keys](https://resend.com/api-keys): create `RESEND_API_KEY`

## Optional

- [React Email](https://react.email/docs/utilities/render.md): render React templates
- [Node SDK repo](https://github.com/resend/resend-node): source and issues