Mattermost is an open source, enterprise-grade messaging platform with thousands of contributors. At Mattermost, we set out to build a platform that would support a variety of extensions. Ranging from simple webhooks accepting curl commands, to bot and integration frameworks, a rich plug-in architecture across server and client experiences, to full access to system APIs with language-specific drivers. All of this is built on top of an open source engine with an open and accessible data model in SQL. We’ll chat about our approach to extending the platform as well as tools, technologies, and best practices for developers writing integrations with our developer toolkit.