---
title: "Establish a WebRTC leg via SDP offer/answer"
method: POST
path: "/webrtc/offer"
tags: ["WebRTC"]
---

# Establish a WebRTC leg via SDP offer/answer

`POST /webrtc/offer`

## Request body

- WebRTCOfferRequest
  - `sdp` string, required — SDP offer from the browser
  - `app_id` string — Application identifier. Carried through to all events emitted for this leg, and matched against the VSI `app_id` filter.
  - `custom_data` unknown

## Response `200`

SDP answer with leg ID

- WebRTCOfferResult
  - `leg_id` string, required
  - `sdp` string, required

## Other responses

- `400` — Invalid JSON or invalid SDP offer
- `500` — Peer connection, track creation, or answer generation failed

## Changes

- **2026-09-01** `89ff267f0958` — 1 info
  - added the new optional request property `custom_data`
- **2026-07-14** `1cf212b29f4e` — 1 info
  - added the new optional request property `app_id`
- **2026-05-11** `7ab34b92424f` — 1 breaking, 1 warning, 2 info
  - removed the required property `status` from the response with the `200` status
  - removed the optional property `instance_id` from the response with the `200` status
  - added the required property `leg_id` to the response with the `200` status
  - added the required property `sdp` to the response with the `200` status
- **2026-03-26** `d09c97c6ca8c` — 1 warning, 1 info
  - removed the request property `app_id`
  - added the optional property `instance_id` to the response with the `200` status
- **2026-03-26** `818619c99a1d` — 2 breaking, 1 info
  - removed the required property `leg_id` from the response with the `200` status
  - removed the required property `sdp` from the response with the `200` status
  - added the required property `status` to the response with the `200` status

[Change history](https://skmtc.dev/voiceblender/apis/voiceblender-api/changes/webrtc/offer/post.md)

---

[API](https://skmtc.dev/voiceblender/apis/voiceblender-api.md) · [All operations](https://skmtc.dev/voiceblender/apis/voiceblender-api/llms.txt) · [OpenAPI document](https://skmtc-service-production.skmtc.workers.dev/v1/apis/voiceblender/voiceblender-api/revisions/89ff267f0958/schema)