# Start building with the Assembly API

Build powerful Custom Apps for private use, Marketplace Apps that are listed in our app store, workflow automations, and more.

## Building blocks for developers

Extend and build on top of every part of the Assembly platform — from internal tools to automations to fully-fledged apps — and create unique experiences for your business or for the thousands of businesses that run on Assembly.

### Apps

Learn how to build an app from scratch, review open-source examples, and learn best practices.

### API Reference

Explore our reference docs to understand core resources like clients, companies, custom fields, and more.

### Developer changelog

Read our changelog to stay up to date on recent changes to Assembly’s API and other developer offerings.