---
ref: company:customer-io
name: Customer.io
tools: [tool:customer-io/create-one-time-send, tool:customer-io/search-people, tool:customer-io/send-transactional-email, tool:customer-io/trigger-broadcast]
tags: [capability:build-audience, capability:send-email, category:email, has:api, has:cli, has:mcp]
updated: 2026-09-27
---

# Customer.io

Messaging automation that sends email, push, SMS and in-app messages from customer data and behavior.

Customer.io is a messaging automation platform: automations, broadcasts,
one-time sends and transactional messages go out by email, push, SMS, in-app
and WhatsApp, targeted with segments built from people's attributes and
events.

The MCP server and the `cio` CLI reach Customer.io's Journeys and Data
Pipelines APIs through generic tools: `cio_schema` finds an endpoint,
`cio_read_api` makes GET requests and `cio_write_api` makes POST, PUT and
PATCH requests (`cio schema` and `cio api <path>` on the CLI). An account
admin must first turn MCP on under Settings > AI; each person then signs in
with OAuth and grants scopes, and changing live data or sending messages over
MCP also needs the admin's permission. The CLI takes a service-account token
(`sa_live_...`) in `CIO_TOKEN`.

The API above is the App API, which sends transactional messages and
broadcasts and reads workspace data with an App API key as a Bearer token.
EU accounts use `https://mcp-eu.customer.io/mcp` and
`https://api-eu.customer.io`. People and events come in through the separate
Track and Pipelines APIs, which use Basic auth.

## Tools

- tool:customer-io/create-one-time-send — Create a one-time send: Creates a one-time send (a newsletter) for a filter over segments and attributes or a CSV of recipients, as a draft, scheduled, or sent right away.
- tool:customer-io/search-people — Search for people: Returns up to 1,000 people in a workspace who match a filter on segment membership and attribute values.
- tool:customer-io/send-transactional-email — Send a transactional email: Sends one transactional email to a person, from a template filled with your message data or from a subject, body and sender you pass, creating the person if needed.
- tool:customer-io/trigger-broadcast — Trigger a broadcast: Sends an API-triggered broadcast now or at a scheduled time, to its saved audience or to the people, emails or filter you pass, with data for its Liquid placeholders.

## Links

- Website: https://customer.io
- Docs: https://docs.customer.io