GitBook is a hosted documentation platform, a web service in which a company writes product guides, help centers and API references and publishes them as a documentation website. GitBook Inc. makes it.
Writers work in a block-based visual editor, or keep the pages as files in a Git repository and sync them with GitHub or GitLab; changes go through change requests that teammates review and merge, much like a pull request for code. GitBook publishes the result as a docs site, which can use the company's own custom domain, and it can generate interactive API documentation. Every published site also gets an MCP server (Model Context Protocol, an interface through which AI assistants read the docs), and paid plans add an AI Assistant that answers readers' questions from the docs and reports on gaps in the content.
GitBook is a subscription service, priced per published site per month plus a charge for each team member. A Free plan for individuals exists; the custom domain, the AI Assistant and site analytics come with the paid plans.