Every public URL that people paste into Slack or LinkedIn needs an Open Graph image. jsontoimg’s path is a signed GET: mint the URL when the page is saved, drop it in og:image, and let the crawler fetch it. You do not have to wait on a webhook to ship the meta tag.
Signed URL, not a screenshot
Screenshot APIs capture whatever is on the page. A named-layer template captures the title, author, and date you send — even if the live layout is a mess. Design 1200×630 once. Name title, author, date (and a cover image if you have one).
Mint an og:image URL
curl -X POST "https://app.jsontoimg.com/api/v1/img/sign" \
-H "Authorization: Bearer $JSONTOIMG_API_KEY" \
-H "Content-Type: application/json" \
-d '{"template":"<design-id>","format":"jpg","layers":{"title":{"text":"Ship the OG tag"}}}'The response is a URL on app.jsontoimg.com. Minting is free. The first unique GET renders and bills one credit to the template owner.
Next.js sketch
const { url } = await client.signImageUrl({
template: process.env.OG_TEMPLATE_ID,
format: "jpg",
layers: { title: { text: post.title }, author: { text: post.author } },
});
// <meta property="og:image" content={url} />Full options, expiry, and batch mint: URL rendering guide. Code-heavy walkthrough: Next.js / WordPress how-to.
What the crawler actually fetches
A crawler arrives with no API key and no session. It reads the tag, GETs the URL, and gives up fast. Two things make that reliable: an absolute URL (relative paths are dropped), and the companion properties from the Open Graph protocol spec — og:image:width and og:image:height. Send the dimensions and the card renders without the crawler measuring the file first.
Design for the crop, not the canvas. 1200×630 is the slot every major network accepts, but LinkedIn and Slack shrink it hard in a feed, so a 28px subtitle disappears. Keep the headline large and the safe area generous. These files get indexed too — Google’s image SEO guidance on filenames and alt text applies to a generated card exactly as it does to a photograph.
Changing the template after URLs are out
A signed URL that omitted a version renders against whatever the template is today. That is fine until someone restyles it and a two-year-old shared link suddenly looks different. Pin a design version on anything you have already published and leave the unpinned URL for drafts. Platforms cache the fetched image on their side anyway, so a redesign will not propagate to old shares — plan for the old look to persist, not for a clean cutover.
Related
- Social share images
- Pricing
- Docs
- How JSON-to-image conversion works
- Open Graph image generator guide
FAQ
How do I put a jsontoimg render in og:image?
Call POST /api/v1/img/sign with the template and layer overrides. Put the returned URL in the og:image meta tag. Crawlers GET it with no API key. The first unique payload costs one credit; the same query string streams the stored file.
Do I need a webhook to generate OG images?
No. Signed URLs are the CMS path. Use POST /api/v1/render?wait=60 only if you want to store the file yourself. Webhooks are for async jobs, not a requirement for meta tags.
What size should the template be?
1200×630 is the usual Open Graph slot. Render PNG or JPG. Pin a design version so a later editor tweak does not change already-shared URLs that omitted version.
Can I mint many OG URLs at once?
POST /api/v1/img/sign with jobs (1–50). That mints URLs; it does not queue POST /api/v1/renders/batch. Loop if you have more than 50 pages.