---
title: "Create a signed multipart part URL"
method: POST
path: "/uploads/{id}/parts"
tags: ["Uploads"]
---

# Create a signed multipart part URL

`POST /uploads/{id}/parts`

Request this immediately before uploading the numbered part. The signed URL expires after 15 minutes. Upload the raw bytes with `PUT`, without a Media Caption API key, and retain the S3 `ETag` response header.

## Request body

- UploadPartUrlRequest
  - `partNumber` integer, required

## Response `200`

Signed part URL created

- UploadPartUrlResponse
  - `partNumber` integer, required
  - `uploadUrl` string, uri, required
  - `expiresInSeconds` integer, required

## Other responses

- `400` — Invalid request
- `401` — Missing or invalid API key
- `404` — Resource not found
- `429` — Rate limit exceeded
- `500` — Internal server error

## Changes

- **2026-08-09** `fff36efa50d3` — 1 info
  - endpoint added

[Change history](https://skmtc.dev/mediacaption/apis/media-caption-public-api/changes/uploads/:id/parts/post.md)

---

[API](https://skmtc.dev/mediacaption/apis/media-caption-public-api.md) · [All operations](https://skmtc.dev/mediacaption/apis/media-caption-public-api/llms.txt) · [OpenAPI document](https://skmtc-service-production.skmtc.workers.dev/v1/apis/mediacaption/media-caption-public-api/revisions/fff36efa50d3/schema)