Guides

Connect an SDK

Point any official Resend SDK at Pretend by changing its base URL.

The base URL

Every official SDK uses the same base URL: http://localhost:3000/, with the scheme and the trailing slash. Most SDKs read it from RESEND_BASE_URL; the Python SDK reads RESEND_API_URL.

Set the API key to Pretend's key: RESEND_API_KEY if you set one, otherwise re_local_dev_key.

Examples

import { Resend } from 'resend';

const resend = new Resend('re_local_dev_key', {
  baseUrl: 'http://localhost:3000/',
});

await resend.emails.send({
  from: 'Acme <onboarding@resend.dev>',
  to: ['delivered@resend.dev'],
  subject: 'It works',
  html: '<p>Captured by Pretend</p>',
});

# export RESEND_API_URL=http://localhost:3000/
import resend

resend.api_key = "re_local_dev_key"

resend.Emails.send({
    "from": "Acme <onboarding@resend.dev>",
    "to": ["delivered@resend.dev"],
    "subject": "It works",
    "html": "<p>Captured by Pretend</p>",
})

<?php
// export RESEND_BASE_URL=http://localhost:3000/
$resend = Resend::client('re_local_dev_key');

$resend->emails->send([
    'from' => 'Acme <onboarding@resend.dev>',
    'to' => ['delivered@resend.dev'],
    'subject' => 'It works',
    'html' => '<p>Captured by Pretend</p>',
]);

# export RESEND_BASE_URL=http://localhost:3000/
require "resend"

Resend.api_key = "re_local_dev_key"

Resend::Emails.send({
  from: "Acme <onboarding@resend.dev>",
  to: ["delivered@resend.dev"],
  subject: "It works",
  html: "<p>Captured by Pretend</p>"
})

// export RESEND_BASE_URL=http://localhost:3000/
package main

import "github.com/resend/resend-go/v2"

func main() {
	client := resend.NewClient("re_local_dev_key")

	client.Emails.Send(&resend.SendEmailRequest{
		From:    "Acme <onboarding@resend.dev>",
		To:      []string{"delivered@resend.dev"},
		Subject: "It works",
		Html:    "<p>Captured by Pretend</p>",
	})
}

Switching per environment

Read the base URL from the environment, so production uses Resend and development uses Pretend with no code change:

.env.development

RESEND_BASE_URL=http://localhost:3000/
RESEND_API_KEY=re_local_dev_key

warning

Include the scheme and the trailing slash. The SDKs join request paths onto this URL, and http://localhost:3000/ is the form every SDK accepts.

Test recipients

Pretend simulates delivery the way Resend does for its test addresses on resend.dev:

Recipient	Outcome
`delivered@resend.dev`	Delivered
`bounced@resend.dev`	Bounced
`complained@resend.dev`	Delivered, then a spam complaint
`suppressed@resend.dev`	Suppressed

Labels work on all but suppressed, such as bounced+signup@resend.dev. Any other recipient is treated as delivered.