---
title: "Send chat message (synchronous)"
method: POST
path: "/agent/v1/chat/{id}/message"
tags: ["Agents"]
---

# Send chat message (synchronous)

`POST /agent/v1/chat/{id}/message`

Sends a message and returns the complete response as a single JSON body. Blocks until the agent turn completes.

**When to use this endpoint:** Best for server-to-server integrations, background processing, or any context where you want the full response in one call without managing an SSE stream.

**Alternatives:**
- `POST /chat/:id/respond` — streaming SSE with normalized events (recommended for custom chat UIs)

## Path parameters

- `id` string, required

## Request body

- object — Message payload following the AI SDK UIMessage format. The body is passed through 1:1 to the underlying chat runtime session. Currently only text parts are supported.
  - `parts` object[] — Message content parts. Currently only "text" type is supported. Additional types (e.g. file, image) may be added in future versions.
    - `type` 'text', required — Part type. Currently only "text" is supported.
    - `text` string, required — The message text content

## Response `200`

Upstream chat runtime response with per-turn usage metadata when available

## Other responses

- `400` — Invalid payload
- `401` — Invalid API key
- `403` — No agent access or non-API-key auth
- `404` — Chat not found
- `409` — Another turn is already in progress for this chat

---

[API](https://skmtc.net/casemark/apis/case-dev-api.md) · [All operations](https://skmtc.net/casemark/apis/case-dev-api/llms.txt) · [OpenAPI document](https://skmtc-service-staging.skmtc.workers.dev/v1/apis/casemark/case-dev-api/versions/5b7e64e6d6f9/schema)