Introduction

Relevant source files

The following files were used as context for generating this wiki page:

• package.json
• readme.md
• src/resend.ts
• src/templates/templates.ts
• src/topics/topics.ts
• src/request-options.spec.ts
• src/batch/batch.spec.ts

The Resend Node.js SDK provides a library for interacting with the Resend API using JavaScript or TypeScript. It manages authentication, request serialization, and response handling for various Resend services including emails, audiences, and contact management.

This SDK requires Node.js version 20 or higher. It supports modern environments through both CommonJS and ESM exports.

Sources: package.json:1-42, readme.md:27-28

SDK Architecture

The SDK follows a modular design centered around the Resend class. This class acts as the main entry point and orchestrates communication with the Resend API. When you instantiate the Resend class, it initializes specialized resource modules that provide methods for specific API features.

Core Components

The following diagram illustrates the relationship between the main SDK class and its resource modules.

The diagram shows the Resend class as the owner of multiple resource-specific classes that encapsulate API logic.

Sources: src/resend.ts:40-75

Setup and Initialization

To use the SDK, you must provide an API key. You can pass this key directly to the constructor or set it via the RESEND_API_KEY environment variable.

1. Import the Resend class.
2. Initialize the class with your API key.
3. Access specific resources (e.g., emails, templates) via class properties.

import { Resend } from 'resend';
const resend = new Resend('re_123456789');

Sources: readme.md:42-45, src/resend.ts:77-94

Configuration Options

The Resend constructor accepts an optional configuration object to customize the SDK's behavior.

Option	Type	Default	Description
baseUrl	string	https://api.resend.com	The base URL for API requests. Can be overridden by RESEND_BASE_URL env var.
userAgent	string	resend-node:[version]	The User-Agent header sent with requests.

Sources: src/resend.ts:31-38, src/resend.ts:96-97

Request Lifecycle and Logic

The SDK uses the fetch API to communicate with Resend servers. The fetchRequest method in the src/resend.ts file manages the core request logic, including error handling and response parsing.

Request Flow

The following flow diagram describes how a request is processed from a resource call to the final response.

The diagram shows the internal validation and error handling logic within the fetchRequest method.

Sources: src/resend.ts:121-209

Advanced Request Options

Every SDK method accepts a RequestOptions object as the final argument. This allows for per-request configuration.

• Idempotency: Pass idempotencyKey to prevent duplicate operations on POST requests.
• Cancellation: Pass an AbortSignal to the signal property to cancel requests or implement timeouts.
• Custom Headers: Pass a headers object to include additional HTTP headers.

Sources: src/resend.ts:212-230, readme.md:120-130, src/batch/batch.spec.ts:98-124

Core Modules Overview

The SDK exposes several modules to manage different aspects of the Resend platform.

Module	Purpose	Key Operations
emails	Send and manage emails	send(), get(), list()
templates	Manage reusable email templates	create(), publish(), duplicate()
apiKeys	Manage access tokens	create(), remove(), list()
segments	Manage contact lists (Audiences)	create(), list(), remove()
inboxes	Manage support inboxes and threads	create(), list(), threads.list()
batch	Send multiple emails at once	send(), create()

Sources: src/resend.ts:47-75, src/request-options.spec.ts:13-149

Conclusion

The Resend Node.js SDK provides a structured, type-safe interface for the Resend API. It abstracts complex networking details such as authentication headers, serialization of React components into HTML, and standardized error reporting, allowing developers to focus on application logic.

Sources: readme.md:47-118, src/resend.ts:121-125