Unfurler Matrix

Per-client behavior for the channels The Lossless Group cares about, ordered by how much we share through each. Use this when you need to debug a specific client or pick which one to test in first.

iMessage (Apple)

• Cache TTL: Days, per exact URL. No public force-refresh.
• Image formats: JPEG ✓, PNG ✓, WebP ✗ (silently dropped on most iOS/macOS versions through 17.x).
• Image size cap: ~5 MB; in practice keep ≤ 500 KB or it’ll skip.
• Required tags: og:title, og:image, og:description. Will fall back to <title> and <meta name="description"> if OG missing.
• Quirks:
  • og:image:secure_url consulted on older iOS; include it.
  • Animated WebP / GIF: GIF works (first frame), WebP does not.
  • Will not render image if Content-Length missing on the image response.
• Force re-unfurl: Append ?v=N to the URL.
• Debug: No native tool. Send to a second device.

WhatsApp

• Cache TTL: ~30 days per URL. No public force-refresh.
• Image formats: JPEG ✓, PNG ✓, WebP ✗ (intermittent).
• Image size cap: Hard ~600 KB ceiling for the preview thumbnail; larger images are skipped, not downscaled.
• Required tags: og:title, og:image. Description optional but recommended.
• Quirks:
  • Unfurls only the first link in a message.
  • Group chats sometimes show the preview to the sender but not all recipients — usually the recipient’s WhatsApp had not crawled the URL yet.
  • Aggressive timeout (~5 s); slow origins fail silently.
• Force re-unfurl: Append ?v=N. Or use a fresh URL.
• Debug: No native tool.

Slack

• Cache TTL: ~22 hours per URL.
• Image formats: JPEG ✓, PNG ✓, WebP ✓ (since 2022, generally fine), GIF ✓.
• Image size cap: ~5 MB.
• Required tags: og:title, og:image, og:description. Falls back to oEmbed if present.
• Quirks:
  • Strict about og:image:type matching the bytes — mismatch is one of the few clients that visibly drops the preview.
  • Honors og:image:width / :height to reserve layout — incorrect values produce visible jank.
  • Will fetch via Slackbot user-agent — ensure this is not blocked by your CDN’s bot rules.
• Force re-unfurl: Type the URL again with a different fragment (#x) or ?v=N.
• Debug: Paste the URL in any channel — preview shows immediately or not at all.

Discord

• Cache TTL: ~24 hours per URL.
• Image formats: JPEG ✓, PNG ✓, WebP ✓, GIF ✓ (animated preserved).
• Image size cap: ~8 MB for embeds.
• Required tags: og:title, og:image. Discord builds rich embeds around og:type=article if article:author and article:published_time are present.
• Quirks:
  • User-agent: Mozilla/5.0 (compatible; Discordbot/2.0; +https://discordapp.com). Some firewalls block this — whitelist if your image 404s in Discord but works elsewhere.
  • og:video produces an inline video player; only set if you actually want that.
• Force re-unfurl: Append ?v=N or wait 24 h.
• Debug: No native tool.

LinkedIn

• Cache TTL: ~7 days per URL.
• Image formats: JPEG ✓, PNG ✓, WebP ✓.
• Image size cap: 5 MB; minimum 1200 × 627 for the large card.
• Required tags: og:title, og:image, og:description, og:url.
• Quirks:
  • Aspect ratio strict: 1.91:1 (1200 × 627–630). Outside that, falls back to small-card layout.
  • Will not re-fetch a URL it has already cached unless forced.
• Force re-unfurl: LinkedIn Post Inspector — paste URL → “Inspect” forces re-scrape.
• Debug: Post Inspector shows what LinkedIn sees.

X / Twitter

• Cache TTL: ~7 days per URL.
• Image formats: JPEG ✓, PNG ✓, WebP ✓ (since 2023).
• Image size cap: 5 MB.
• Required tags: twitter:card, twitter:title, twitter:image. Falls back to OG tags if Twitter-specific missing.
• Quirks:
  • twitter:card=summary_large_image requires image ≥ 300 × 157 and ≤ 5 MB at aspect ratio 2:1 (so 1200 × 600 or 1200 × 630 both work).
  • The standalone Twitter Card Validator is gone — only inline-preview testing on x.com works now.
• Force re-unfurl: Append ?v=N.
• Debug: Compose a tweet (do not send) — preview renders below the textarea.

Facebook

• Cache TTL: ~30 days per URL.
• Image formats: JPEG ✓, PNG ✓, WebP ✓.
• Image size cap: 8 MB; minimum 200 × 200, recommended 1200 × 630.
• Required tags: og:title, og:image, og:url, fb:app_id (optional but recommended for ownership).
• Force re-unfurl: Facebook Sharing Debugger — paste URL → “Scrape Again”.
• Debug: Sharing Debugger shows the canonical scrape result and any warnings.

Generative engines (GEO)

These don’t “unfurl” but they consume the same metadata when surfacing your page in answers.

Allow these in robots.txt if you want to be cited. Block them if you don’t. Default Astro Knots policy: allow.

Decision tree: which client to test first?

1. Sharing primarily through iMessage / WhatsApp? → Test there first; everything else is easier.
2. Sharing primarily through Slack / Discord? → Test there; debuggers are harder to get to than Slack itself.
3. Marketing reach through LinkedIn / X / Facebook? → Use their debuggers to force a re-scrape after every change. They cache long.
4. Concerned about generative-engine citation? → Validate JSON-LD with Schema.org validator and Google Rich Results Test.

When in doubt: the curl triplet

# What does the unfurler get when fetching the page HTML?
curl -sA "Mozilla/5.0 (compatible; Slackbot-LinkExpanding 1.0)" "<page-url>" | grep -iE 'og:|twitter:|<title>'

# What does the unfurler get when fetching the OG image?
curl -sIA "Mozilla/5.0 (compatible; facebookexternalhit/1.1)" "<og-image-url>"

# What does a no-Accept-header client (most unfurlers) actually receive?
curl -sI "<og-image-url>" | grep -iE 'content-type|content-length|vary'

The third line is the one that catches the ImageKit / WebP-versus-JPEG content-negotiation gotcha that bit us on content-farm.