Gatsby is a free, open-source framework for building websites and web apps with React, the JavaScript library for building user interfaces. It is known as a static site generator: a build tool that produces finished HTML pages in advance, so that a CDN (content delivery network) can serve them without running server code for each visit. The project is developed by the Gatsby community and Gatsby, Inc.; Gatsby Cloud, the company's hosting service, is merging into Netlify.
Source plugins pull content from Markdown files, a headless CMS such as Contentful or WordPress, or a REST or GraphQL API into one GraphQL data layer, which the pages query when the site is built. Each page can use static site generation, deferred static generation or server-side rendering. Gatsby automates code splitting, image optimization, inlining of critical styles, lazy loading and prefetching. Every Gatsby site is also a full React app, so pages stay interactive in the browser.
Gatsby is released under the MIT license and is free. Sites built with it can be hosted on a CDN or a static hosting service.