link-preview-check

scripts/preview-check.mjs is zero-dependency Node 22+. It makes plain HTTP requests only, no browser.

node preview-check.mjs https://example.com
node preview-check.mjs https://example.com /about /pricing /blog/post-1    # several routes (catches SPA duplicates)
node preview-check.mjs --sitemap https://example.com/sitemap.xml            # up to 50 URLs (follows a sitemap index)
node preview-check.mjs https://example.com --out previews.html

It prints problems (✘) and warnings (!) per URL and exits 1 if there are problems. It also writes link-preview.html with approximate WhatsApp, LinkedIn, X and Facebook cards. Open it and look. In Git Bash on Windows, MSYS rewrites /about into a file path; the script undoes that (a one-letter path like /p comes back as /p/). Full URLs or MSYS_NO_PATHCONV=1 always work.

Always check several routes

Pass the home page and 2–3 inner pages. The most common failure on modern sites: a single-page app ships one index.html, so every route has the homepage's title and image, and the real titles are set by JavaScript, which crawlers never run.

Fix recipes

• No og:image / weak card. Add these to every page (absolute URLs):

  <meta property="og:title" content="Page title">
  <meta property="og:description" content="One or two sentences.">
  <meta property="og:url" content="https://example.com/page">
  <meta property="og:image" content="https://example.com/og/page.jpg">
  <meta property="og:image:width" content="1200"><meta property="og:image:height" content="630">
  <meta name="twitter:card" content="summary_large_image">

  Image: 1200×630 JPG or PNG, ideally under 300 KB (WhatsApp drops heavy images), with key content away from the edges because some apps crop to a square. Generate cards with PIL or any image tool. SVG never works.
• SPA with the same title everywhere. Emit a static HTML copy per route at build time with that route's tags. For Vite: a plugin with enforce: 'post' whose generateBundle reads bundle['index.html'], swaps the meta block, and this.emitFiles about.html, blog/post.html and so on. Cloudflare Pages, Netlify and Vercel serve about.html at /about, and static files take precedence over the SPA fallback rewrite. Next.js, Nuxt, Astro and SvelteKit do this natively through their metadata/head APIs with SSR or SSG.
• Relative og:image. Make it absolute: https://domain/og/x.jpg.
• twitter:card = summary. Use summary_large_image for the big card.

After fixing

Platforms cache previews. Ask the user to refresh them: LinkedIn Post Inspector (linkedin.com/post-inspector) and the Facebook Sharing Debugger (developers.facebook.com/tools/debug) both force a re-scrape. WhatsApp and X refresh on their own after a while, and a link with a new query string (?v=2) shows the new card right away.