Set a YouTube thumbnail through the API or an AI agent

Yes. When you create the post, add a cover_photo with a public url to a JPG or PNG. On YouTube we send it as the custom thumbnail. YouTube only accepts custom thumbnails on phone-verified channels.

Steps (API)#

1. Upload your video and get its media id.
2. Create the post with media_ids and a cover_photo:

{
  "content": "Our new video",
  "account_ids": [123],
  "media_ids": ["<video media id>"],
  "cover_photo": { "url": "https://example.com/thumb.jpg" }
}

3. Check the response notes. If the thumbnail could not be set, the note says why.

Steps (AI agent)#

Ask the agent to create the post and give it the image link. The create_post tool has the same cover_photo field with url or media_id.

Details#

• cover_photo.media_id also works with an image already in your media library. Some stored images can only be shared as a link that lasts 7 days, so for a post scheduled further out than that, send url instead. The response notes tell you when this applies.
• You can also set it inside the YouTube settings as platform_content.youtube.settings.coverPhotoUrl. It is the same thing.
• The thumbnail is set when the post is created. Editing a scheduled post through the API or an agent does not change the cover. Editing a scheduled post in the app changes only its text and time. To change the cover, right-click the post on the calendar, choose Duplicate, click Select Cover Photo under the video preview, schedule the copy and delete the original.
• YouTube's own API does not allow setting paid promotion, age restriction, comments, Shorts remixing or caption certification. Those stay in YouTube Studio.