---
title: "Add Message"
method: POST
path: "/agent/sessions/{session_id}/messages"
---

# Add Message

`POST /agent/sessions/{session_id}/messages`

Persist one rendered message (user text or assistant parts) to a session.

## Path parameters

- `session_id` string, required

## Request body

- AddMessageRequest — Body for persisting one rendered message.
  - `role` string, required
  - `content` object, required

## Response `200`

Successful Response

- AgentMessage — A persisted message in a session; ``content`` is the rendered parts.
  - `id` string, required
  - `session_id` string, required
  - `role` string, required — user | assistant | system
  - `content` object, required
  - `created_at` string, date-time, required

## Other responses

- `422` — Validation Error

---

[API](https://skmtc.dev/ionworks/apis/fastapi.md) · [All operations](https://skmtc.dev/ionworks/apis/fastapi/llms.txt) · [OpenAPI document](https://skmtc-service-production.skmtc.workers.dev/v1/apis/ionworks/fastapi/revisions/7337a3cbdaf2/schema)