Outputs

The output parameter of POST /design tells Rivermark what frames to produce. It takes either a list of expected outputs, or a single render format.

Named outputs

When your code needs to know exactly what came back — which is nearly always in production — declare each expected output with an ID. Each entry may include a size, a human-readable description of what the frame is for, and a per-frame format:

Three declared outputs

"output": [
  { "id": "instagram_story_1", "size": "1080x1920" },
  { "id": "instagram_story_2", "size": "1080x1920" },
  { "id": "blog_post_header", "size": "1600x900", "format": "webp" }
]

The response's output array maps back to those IDs, so you can programmatically handle multiple outputs:

Response

{
  "design_id": "rmd_cj4hbqz2w0003mz6x7p9q2xe",
  "output": [
    {
      "id": "instagram_story_1",
      "url": "https://cdn.rivermark.ai/rmd_cj4hbqz2w0003mz6x7p9q2xe/k3f8qz1w/instagram_story_1.png",
      "format": "png",
      "width": 1080,
      "height": 1920
    },
    {
      "id": "instagram_story_2",
      "url": "https://cdn.rivermark.ai/rmd_cj4hbqz2w0003mz6x7p9q2xe/k3f8qz1w/instagram_story_2.png",
      "format": "png",
      "width": 1080,
      "height": 1920
    },
    {
      "id": "blog_post_header",
      "url": "https://cdn.rivermark.ai/rmd_cj4hbqz2w0003mz6x7p9q2xe/k3f8qz1w/blog_post_header.webp",
      "format": "webp",
      "width": 1600,
      "height": 900
    }
  ],
  "…": "…"
}

Each output entry:

Prop

Type

Bare formats

If you pass just a format string — "png", "jpeg", "webp", "pdf", or "html" — you'll receive all created and edited frames in that format, without IDs. This is handy for quick one-off requests:

All frames as PNG

"output": "png"

Omitting output entirely is equivalent to "png".

Formats

Format	Use
`png`	Default. Lossless, best for design output with flat colors and text.
`jpeg`	Smaller files for photographic content.
`webp`	Modern web delivery, smaller than both at similar quality.
`pdf`	Print and document workflows; one page per frame.
`html`	The live HTML document itself — every frame, fully self-contained.

Ephemeral URLs, downloadable sources

Rendered URLs are temporary. When a design completes, download anything you need to keep:

TypeScript — download every output

for (const frame of design.output) {
  const res = await fetch(frame.url);
  await writeFile(`${frame.id}.${frame.format}`, Buffer.from(await res.arrayBuffer()));
}

The changes list additionally includes the created and edited HTML sources and generated images, each with its own temporary URL — useful if you want to host or post-process the HTML itself (see the API reference).

Multi-format requests

One request can produce frames in different sizes and formats — include size and format per output entry. The resizing guide covers reflow-aware adaptation in depth.