asset_create_upload
Reserve an Asset and get a short-lived URL to upload the file to. Step one of bringing your own creative in.
Reserves an Asset and returns a short-lived, presigned URL to upload the file to. This is step one of the upload flow; see Bring your own creative for the whole sequence.
Input
| Field | Type | Required | Description |
|---|---|---|---|
filename |
string |
yes | The original filename, including extension. |
Output
{ assetId, uploadUrl, expiresAt }:
| Field | Type | Description |
|---|---|---|
assetId |
ast_* |
The reserved Asset id — pass it to asset_finalize. |
uploadUrl |
string |
A presigned PUT URL. Send the file bytes here. |
expiresAt |
number |
Epoch ms when uploadUrl stops working. |
The agent uploads the bytes itself
Send an HTTP PUT to uploadUrl with the file as the request body and its
Content-Type set. The bytes must never pass through the conversation — the
agent reads the file and PUTs it from its own runtime.
PUT <uploadUrl>
Content-Type: image/png
<the file bytes>Once the PUT returns 200, call asset_finalize.
Requires outbound network access
The PUT targets *.r2.cloudflarestorage.com. If the agent’s runtime
restricts network access, that host must be allowed or the upload can’t
complete.
Example
“Add this logo.png to our creative library.”
Claude calls asset_create_upload({ filename: 'logo.png' }), PUTs the file to
the returned uploadUrl, then finalizes with the returned assetId.
Errors
- The file’s type and size aren’t checked here — nothing is known until the
bytes arrive, so rejection happens at
asset_finalize. 401 Unauthorized— token expired or missingasset:write.