# Customer.io Documentation

> Customer.io is a messaging automation platform for sending targeted email, push notifications, SMS, in-app messages, and webhooks based on customer behavior and data attributes. These docs cover setup, integration, messaging, segmentation, analytics, API reference, and agent-native access through the Customer.io CLI or MCP server.

## When to use this documentation

Customer.io decides who gets a message, what it says, and when it sends. Read these docs when the task in front of you is one of these:

- [Send a message from your own code](https://docs.customer.io/messaging/send/transactional/api.md): Transactional email, push, SMS, and WhatsApp. These are the messages you address to one person and trigger yourself.
- [Get profile and event data in](https://docs.customer.io/integrations/data-in/getting-started.md): Identify people, record what they do, and relate them to objects like accounts or carts.
- [Build something that sends on its own](https://docs.customer.io/messaging/send/automations/overview.md): Automations that react to an event, a segment, or a schedule without you calling an API each time.
- [Add Customer.io to a mobile or web app](https://docs.customer.io/integrations/sdk.md): The iOS, Android, React Native, Flutter, and JavaScript SDKs, including push and in-app messages.
- [Send delivery and engagement data somewhere else](https://docs.customer.io/integrations/data-out/getting-started.md): Reporting webhooks, warehouse syncs, and the destinations Data Pipelines writes to.
- [Work out which API to call](https://docs.customer.io/integrations/api/customerio-apis.md): What the Track, App, and Data Pipelines APIs each do, and which one a given task belongs to.

### How to read these docs

- Add `.md` to any documentation URL to get its Markdown source: `https://docs.customer.io/get-started/quick-start-guide.md`. Requesting a page with `Accept: text/markdown` redirects to the same thing.
- Every section below has its own `llms.txt` naming each page in it, so you can read one area without loading the whole site.
- [`/openapi.json`](https://docs.customer.io/openapi.json) describes the Track and App APIs together, with the base URL each path answers on. [`/.well-known/api-catalog`](https://docs.customer.io/.well-known/api-catalog) lists every OpenAPI description this site publishes.
- A request for a page that does not exist answers `Accept: application/json` with a structured error carrying a code, a message, and links back to these indexes.

Customer.io documentation is organized into the following sections. Each section has its own `llms.txt` file with detailed page listings.

## Sections

- [AI features](https://docs.customer.io/ai/llms.txt): AI features documentation (22 pages)
- [Get started](https://docs.customer.io/get-started/llms.txt): Get started documentation (9 pages)
- [Integrations](https://docs.customer.io/integrations/llms.txt): Integrations documentation (768 pages)
- [Messaging](https://docs.customer.io/messaging/llms.txt): Messaging documentation (357 pages)
- [Settings & billing](https://docs.customer.io/accounts/llms.txt): Settings & billing documentation (39 pages)

## Additional resources

- [Customer.io CLI](https://docs.customer.io/ai/cli/get-started.md): Install the `customerio/cli` agent skill and let terminal-based coding agents sign up, authenticate, and manage Customer.io workspaces
- [Customer.io MCP](https://docs.customer.io/ai/mcp/get-started.md): Connect chat-based AI tools like ChatGPT and Claude Desktop to Customer.io
- [Full documentation](https://docs.customer.io/llms-full.txt): Complete text of all documentation pages in a single file
- [Customer.io API spec](https://docs.customer.io/openapi.json): Primary OpenAPI spec for the Track (ingress) and App APIs together, at the conventional path
- [Pipelines API spec](https://docs.customer.io/files/pipelines.json): OpenAPI spec for the Data Pipelines API
- [Track API spec](https://docs.customer.io/files/journeys-track.json): OpenAPI spec for the Track API
- [App API spec](https://docs.customer.io/files/journeys-app.json): OpenAPI spec for the App API
- [Webhooks spec](https://docs.customer.io/files/journeys-webhooks.json): OpenAPI spec for reporting webhooks