Image: resolve URLs to base64

What it does

This transform downloads request or response image URLs concurrently and replaces them with inline base64 sources. A failed or oversized download leaves that node unchanged.

Without this transform, Monoize never fetches remote image URLs.

Reference

Property	Value
Type ID	`image_resolve_urls`
Phase	`request`, `response`
Scopes	Provider, API key

When to use

The upstream rejects URL image sources and accepts only inline base64 data.
Image URLs point to hosts that the upstream cannot reach, for example an internal network.

Configuration

Option	Type	Required	Default	Description
`timeout_seconds`	integer	No	`30`	Per-download timeout in seconds.
`max_bytes`	integer	No	`20971520`	Maximum bytes per downloaded image. Default 20 MiB.
`roles`	string[]	No	—	Roles whose image URLs are resolved: `user`, `assistant`, `system`. Empty resolves all.

Example rule

{
  "transform": "image_resolve_urls",
  "enabled": true,
  "phase": "request",
  "models": [
    "*"
  ],
  "config": {
    "timeout_seconds": 30,
    "roles": [
      "user"
    ]
  }
}

Return base64 images to downstream clients

For an Images API client that requires b64_json, apply the transform in the response phase. Monoize downloads the upstream URL and encodes the image as data[].b64_json.

{
  "transform": "image_resolve_urls",
  "enabled": true,
  "phase": "response",
  "models": [
    "gpt-image-2.5-sunburst"
  ],
  "config": {
    "timeout_seconds": 30,
    "max_bytes": 20971520,
    "roles": [
      "assistant"
    ]
  }
}