# MessageFlow API

> Documentation site for the MessageFlow API, a JSON REST API for sending and tracking email, SMS, and other channels. This host publishes API v2.1 and API v3.0. The OpenAPI files are the contract. The guide links are markdown and can be read without running this site's JavaScript.

Requests use `Authorization` and `Application-Key` from the MessageFlow panel. The API host is `https://api.messageflow.com`. Version 2.1 paths look like `/v2.1/...`. Version 3.0 paths look like `/v3.0/...`. On this site those contracts are browsable at `/v2` and `/v3`, and downloadable as the files below. The same narrative pages are inlined in `/llms-full.txt`.

## API reference

- [API v2.1 OpenAPI (YAML)](/v2/openapi.yaml): Full v2.1 contract, including schemas, operations, and the narrative pages rendered in the v2 docs.
- [API v2.1 OpenAPI (JSON)](/v2/openapi.json): The same v2.1 contract in JSON, for Postman, Insomnia, or generated clients.
- [API v3.0 OpenAPI (YAML)](/v3/openapi.yaml): Full v3.0 contract, including RCS and SMS webhooks.
- [API v3.0 OpenAPI (JSON)](/v3/openapi.json): The same v3.0 contract in JSON.

## Guides

- [Introduction (v2)](/v2/guides/introduction.md): Response envelope (`meta`, `data`, `errors`), pagination, and how to read the v2.1 reference.
- [Authentication (v2)](/v2/guides/authentication.md): How to send `Authorization` and `Application-Key`, and what an unauthorized response looks like.
- [Quick start (v2)](/v2/guides/quick-start.md): Shortest path to a first successful v2.1 call.
- [Introduction (v3)](/v3/guides/introduction.md): What v3.0 covers, the base URL, and where the downloadable spec lives.
- [Authentication (v3)](/v3/guides/authentication.md): The same two headers on v3.0, plus permission and allowlist errors.
- [Request and response format (v3)](/v3/guides/request-and-response-format.md): JSON bodies, gzip requests, the response envelope, and pagination on v3.0.
- [Webhook overview (v3)](/v3/guides/webhook-overview.md): How RCS and SMS webhooks are delivered and how to acknowledge them.

## Optional

- [Error codes (v3)](/v3/guides/error-codes.md): Machine-readable error codes returned by v3.0.
- [What's new in v3](/v3/guides/whats-new-in-v3.md): What changed from the previous API version, including the RCS channel.
- [MCP integration (v3)](/v3/guides/mcp-integration.md): Tools an MCP client can call against this API, and when a tool is hidden.
- [MCP integration (v2)](/v2/guides/mcp-integration.md): The same MCP server and tools as used against the v2.1 contract.
- [Incoming webhooks (v2)](/v2/guides/incoming-webhooks.md): v2.1 webhook payloads for email, SMS, push, and campaigns.
- [Long-running actions (v2)](/v2/guides/long-running-actions-retry-after.md): How a v2.1 call uses HTTP 202 and the `Retry-After` header.
- [Dynamic email content (v2)](/v2/guides/dynamic-e-mail-content.md): Placeholders that fill one email template per recipient.
- [SMS billing (v2)](/v2/guides/sms-billing.md): How GSM-7 and other characters change the number of SMS segments.
- [Migration to v2.1](/v2/guides/migration-to-newest-version.md): What moved when older v1 and v2 endpoints were discontinued.
- [RCS delivery reports (v3)](/v3/guides/rcs-delivery-reports.md): Delivery, non-delivery, and expiry events for an outbound RCS message.
- [RCS engagement reports (v3)](/v3/guides/rcs-engagement-reports.md): Clicks and other engagement events for an RCS message.
- [RCS incoming messages (v3)](/v3/guides/rcs-incoming-messages.md): RCS messages a subscriber sends back, including suggested replies.
- [SMS delivery reports (v3)](/v3/guides/sms-delivery-reports.md): Delivery and non-delivery of an outbound SMS, including Flash SMS.
- [SMS link clicks (v3)](/v3/guides/sms-link-clicks.md): Clicks on links tracked in an SMS.
- [SMS incoming messages (v3)](/v3/guides/sms-incoming-messages.md): SMS messages a subscriber sends back.