A YouTube thumbnail generator is one template and one JSON object per video. jsontoimg fills the episode title, guest name, and a photo on named layers, then returns a JPG or PNG ready to upload. It suits channels with a repeating format: interviews, weekly recaps, course lessons, release notes.
Layers that change per video
title: the short hook, not the full video titleepisode: a number or date badgeguest_nameandguest_photo: the photo layer takes a publichttpsfile ending.png,.jpg,.jpeg, or.webplogo: constant, so keep it in the design and not in the payload
What YouTube asks for
YouTube’s custom thumbnail help asks for JPG or PNG files, a 16:9 aspect ratio for standard videos, and a file under 2 MB when uploading from mobile. Design the template at 16:9 and request jpg if file size matters, since format and scale are request fields.
Render one thumbnail
curl -X POST "https://app.jsontoimg.com/api/v1/render?wait=60" \
-H "Authorization: Bearer $JSONTOIMG_API_KEY" \
-H "Content-Type: application/json" \
-d '{"template":"<design-id>","format":"jpg","layers":{"title":{"text":"Why we deleted our staging server"},"episode":{"text":"EP 42"}}}'For a season, put the rows in a sheet and use the Google Sheets add-on to render 50 at a time, or loop batches of 50 from a script.
What it does not do
jsontoimg does not upload to YouTube, pick a frame from your video, or predict click-through. It produces a consistent design from your data. Test two template layouts on real videos and keep the one your audience clicks.
Keep the series recognisable
A consistent layout across a series is the point of a template. Lock the logo, colours, and type in the design. Let only the hook, number, and photo change. Check the headline at the small size a thumbnail is shown in a feed, not at full size in the editor.
Related
FAQ
What is a YouTube thumbnail generator?
A tool that builds a thumbnail from a template and per-video data. jsontoimg fills a title, episode number, and guest photo on named layers and returns a JPG or PNG.
What format and ratio does YouTube want?
YouTube’s help page asks for JPG or PNG, a 16:9 aspect ratio for standard videos, and under 2 MB when uploading from mobile.
Does jsontoimg upload thumbnails to YouTube?
No. It returns an image file or signed URL. You upload it yourself or with your own script.
How many thumbnails can I render at once?
A batch holds 50 jobs. A 200-video backlog is four batches, and failed jobs are free to retry.