Introduction

The Substack API client is a modern, type-safe TypeScript library that provides a comprehensive interface for interacting with Substack's platform. Whether you're building automation tools, analytics dashboards, content management systems, or social features, this library makes it easy to integrate with Substack.

Who This Is For

Content Creators & Publishers

Newsletter automation - Schedule posts, manage drafts, track engagement
Audience analytics - Monitor follower growth, engagement rates, content performance
Content distribution - Cross-post to multiple publications, manage syndication
Community management - Moderate comments, engage with readers, build relationships

Developers & Technical Teams

API integration - Clean, typed interface for Substack's APIs
Automation workflows - Build custom publishing pipelines and content workflows
Data analysis - Extract insights from publication data and reader behavior
Custom applications - Build newsletter management tools, reader apps, content discovery platforms

Data Analysts & Marketers

Performance tracking - Monitor post performance, engagement metrics, growth trends
Audience insights - Understand reader behavior, preferences, and engagement patterns
Competitive analysis - Track industry publications and benchmark performance
Growth optimization - Identify high-performing content patterns and engagement strategies

Marketing & Growth Teams

Lead generation - Integrate newsletter signups with CRM systems and marketing funnels
Email marketing - Coordinate Substack content with broader email marketing campaigns
Social media - Automate social sharing and cross-platform content promotion
Analytics integration - Connect Substack data with Google Analytics, Mixpanel, and other tools

Key Features

🏗️ Modern Entity Model

Navigate Substack data naturally with object-oriented entities:

// Fluent navigation through relationships
for await (const post of profile.posts()) {
  for await (const comment of post.comments()) {
    await comment.like();
  }
}

🔄 Seamless Pagination

Automatic pagination handling with async iterators:

// No manual pagination - just iterate
for await (const post of profile.posts()) {
  console.log(post.title); // Handles all pages automatically
}

🛡️ Complete Type Safety

Full TypeScript support with comprehensive type definitions:

// Everything is typed - IDE autocomplete and compile-time checks
const profile: Profile = await client.profileForSlug('username');
const post: Post = await profile.posts({ limit: 1 }).next().value;

🔐 Secure Authentication

Cookie-based authentication using your Substack session:

const client = new SubstackClient({
  token: 'your-connect-sid-cookie-value' // Extracted from browser
});

📝 Content Creation & Management

Full CRUD operations for posts, notes, and comments:

const myProfile = await client.ownProfile();

// Create content
await myProfile.createPost({ title: 'New Article', body: '...', isDraft: false });
await myProfile.createNote({ body: 'Quick thought...' });

// Social interactions  
await post.like();
await post.addComment('Great insights!');
await profile.follow();

Complete social interaction capabilities: - Like posts, notes, and comments - Follow and unfollow users - Add comments and engage in discussions - Track follower relationships and social connections

📊 Analytics & Insights

Built-in support for tracking engagement and performance:

// Get comprehensive analytics
const reactions = post.reactions?.length || 0;
const comments = post.commentCount;
const followers = profile.followerCount;

🚀 High Performance

Optimized for efficiency with intelligent caching and request batching: - In-memory caching for frequently accessed data - Intelligent pagination to minimize API calls - Async iteration for memory-efficient processing of large datasets

Architecture Overview

The library is built around several key concepts:

SubstackClient

The main entry point that handles authentication and provides access to entities:

const client = new SubstackClient({ token: 'cookie-value' });

Entity Classes

Represent Substack objects with navigation and interaction methods: - Profile - User profiles with read access to their content - OwnProfile - Your authenticated profile with content creation capabilities
- Post - Long-form articles and newsletters - Note - Short-form social content - Comment - Comments on posts and notes

Async Iterators

Provide seamless pagination for collections:

// All collections support async iteration
profile.posts()      // AsyncIterable<Post>
post.comments()      // AsyncIterable<Comment>  
profile.notes()      // AsyncIterable<Note>

Type Safety

Comprehensive TypeScript definitions ensure compile-time safety:

interface Profile {
  id: number;
  name: string;
  slug: string;
  followerCount: number;
  posts(options?: { limit?: number }): AsyncIterable<Post>;
}

Use Case Examples

const myProfile = await client.ownProfile();

// Track performance metrics
for await (const post of myProfile.posts({ limit: 10 })) {
  console.log(`"${post.title}": ${post.reactions?.length || 0} reactions`);
}

Content Curation Bot

// Find and engage with trending content
for await (const user of myProfile.following()) {
  for await (const post of user.posts({ limit: 3 })) {
    if ((post.reactions?.length || 0) > 10) {
      await post.like();
      await post.addComment('Great insights!');
    }
  }
}

Cross-Platform Publishing

// Publish to Substack and sync elsewhere
const post = await myProfile.createPost({
  title: 'New Article',
  body: content,
  isDraft: false
});

// Sync to other platforms
await syncToMedium(post);
await shareOnTwitter(post.canonicalUrl);

Community Engagement Tracker

// Monitor community activity
for await (const post of myProfile.posts()) {
  for await (const comment of post.comments()) {
    if (needsResponse(comment)) {
      await comment.addComment(generateResponse(comment));
    }
  }
}

Getting Started

Install the library: npm install substack-api
Get your authentication cookie from your browser's Substack session
Initialize the client with your credentials
Start exploring with the entity model

import { SubstackClient } from 'substack-api';

const client = new SubstackClient({
  token: process.env.SUBSTACK_TOKEN!
});

// Test connection
const isConnected = await client.testConnectivity();

// Get your profile and start exploring
const myProfile = await client.ownProfile();
console.log(`Welcome ${myProfile.name}!`);

What Makes This Different

Entity-Oriented Design

Unlike traditional REST clients that return raw JSON, this library provides rich entity objects with built-in navigation and interaction methods.

Developer Experience First

Intuitive async iteration patterns
Comprehensive TypeScript support
Intelligent error handling and retry logic
Extensive documentation with real-world examples

Production Ready

Robust error handling for network issues and API changes
Efficient memory usage for large datasets
Rate limiting and request optimization
Comprehensive test coverage

Community Focused

Open source with active development
Responsive to user feedback and feature requests
Comprehensive documentation and examples
Regular updates to support new Substack features

The Substack API client makes it easy to build powerful applications on top of Substack's platform. Whether you're automating your newsletter workflow, building analytics tools, or creating new ways for creators to engage with their audience, this library provides the foundation you need.