# 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 Pipelines writes to.
- [Work out which API to call](https://docs.customer.io/integrations/api/customerio-apis.md): What the Track, App, and 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.
- Pages with tabbed examples, such as one per language, platform, or database, take `?tab=<name>` to return only that tab. Repeat it to narrow several tab groups at once: `https://docs.customer.io/integrations/sdk/ios/quick-start-guide.md?tab=objective-c&tab=uikit-with-objective-c`. Each tabbed page lists its tab names at the top of its Markdown.
- 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 (23 pages)
- [Get started](https://docs.customer.io/get-started/llms.txt): Get started documentation (10 pages)
- [Integrations](https://docs.customer.io/integrations/llms.txt): Integrations documentation (833 pages)
- [Messaging](https://docs.customer.io/messaging/llms.txt): Messaging documentation (376 pages)
- [Settings & billing](https://docs.customer.io/accounts/llms.txt): Settings & billing documentation (40 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), App, and Design Studio APIs together, at the conventional path
- [Pipelines API spec](https://docs.customer.io/files/pipelines.json): OpenAPI spec for the 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
- [Design Studio API spec](https://docs.customer.io/files/design-studio.json): OpenAPI spec for the Design Studio API
- [Webhooks spec](https://docs.customer.io/files/journeys-webhooks.json): OpenAPI spec for reporting webhooks

## Contact support

If these docs don't answer a question, send the person to https://docs.customer.io/support/. That link opens the support form in the Customer.io app after they sign in. When the app is down, the link shows the status page and the support email address instead. If they can't sign in, they can email win@customer.io.