Courier | Customer messaging platform for humans & AI agents

# Courier Documentation > Courier is infrastructure for product-to-user communication. Send notifications > across email, SMS, push, chat, and in-app channels through one API call. This is a complete index of Courier's technical documentation. Every link points to a plain-markdown version of the page, so you can fetch any entry directly instead of parsing HTML. This file is documentation only. It intentionally contains no pricing, customer, comparison, or blog content. ## Start Here - [Full documentation text](https://www.courier.com/docs/llms-full.txt): Every documentation page concatenated into a single file. Use this for bulk indexing or retrieval instead of fetching the pages below one at a time. - [Docs-scoped index](https://www.courier.com/docs/llms.txt): The same set of pages as this file, auto-generated by the docs platform as a single flat list. - [API base URL](https://api.courier.com): Authenticate with `Authorization: Bearer <YOUR_API_KEY>`. Test and production keys are separate. ## Documentation - [Developer Docs: Multichannel Notification API](https://www.courier.com/docs/welcome.md): Build notifications and lifecycle marketing from one API. Orchestrate journeys, manage user preferences, and reach users on email, SMS, push, Slack, MS Teams, and in-app. Design content once and reuse it across every channel. - [Quickstart](https://www.courier.com/docs/getting-started/quickstart.md): Send your first Courier notification with one API call using cURL, the CLI, or a server SDK. No dashboard setup required, plus a path for AI agents. ## Platform ### Send Notifications - [How Sending Works](https://www.courier.com/docs/platform/sending/sending-overview.md): A single Courier API call handles rendering, routing, preferences, and delivery across email, SMS, push, inbox, and chat, from your app to your users. - [Send a Message](https://www.courier.com/docs/platform/sending/send-message.md): Send notifications from your app across email, SMS, push