Pinterest Pin limits: title 100, description 800, alt text 500

The Pinterest API v5 caps a Pin's title at 100 characters, its description at 800, its alt text at 500 and its link at 2048. If you generate images in bulk, write the copy for these fields at the same time, because a Pin create call with an over-length field is rejected.

What are the limits?

They are maxLength values in the Pinterest OpenAPI description for the Pin models. Title and alt text are nullable, so you may leave them out.

How should I write alt text for a generated image?

Describe what is visible, in plain terms, and stay well under 500. Put the subject first. Alt text is separate from the AI disclosure; set ai_disclosures as well when the image is AI-made.

How do I keep copy and image in step?

Generate the image and the copy in one pass. Request the image with the images API, and store the prompt, alt text and title together so that a later regeneration updates all three.

import json, os, urllib.request

body = {
    "model": "bytedance-seed/seedream-4.5",
    "prompt": "cozy reading nook with a green armchair and a lamp, warm tones",
    "aspect_ratio": "2:3",
    "output_format": "jpeg"
}
req = urllib.request.Request(
    "https://api.sume.com/v1/images",
    data=json.dumps(body).encode(),
    headers={
        "Authorization": "Bearer " + os.environ["SUME_API_KEY"],
        "Content-Type": "application/json",
    },
    method="POST",
)
print(urllib.request.urlopen(req).read().decode())

What else should I check?

Verify the limits in the live spec at integration time. The images guide lists Sume's parameters.