ABOUT THIS EPISODE
https://page2pod.com - JavaScript isn't breaking your SEO — rendering is. Merj R&D Director Giacomo Zecchini on what Google and AI crawlers actually see.
Giacomo Zecchini has spent years injecting tracking beacons into Google's rendering service to replace industry folklore with data. His research with Vercel found that virtually every indexable page crawled by Googlebot gets rendered — so the "rendering budget" most SEOs plan around doesn't behave the way the industry assumes. The real failures live in implementation: APIs timing out mid-render, lazy-loaded content that never fires under Google's viewport expansion, and hero images that shove main content thousands of pixels down the page.
Do AI crawlers render JavaScript? Some can — but none do it consistently. Giacomo's testing shows bots like ClaudeBot, Mistral, and DuckAssistBot sometimes render and sometimes fetch raw HTML using the same user agent, which is why Answer Engine Optimization (AEO) starts with content that survives a no-render fetch. He also makes the case for serving Markdown to bots via the Accept HTTP header (a web standard) instead of .md URLs, and shows how one swapped ARIA label made ChatGPT's agent click Cancel instead of Save — turning accessibility into an agentic-web requirement, not a nice-to-have.
⚙️ In This Episode
- Why "JavaScript problems" are really rendering and implementation problems
- The rendering budget myth, tested against live Googlebot data
- How does Google's viewport expansion handle lazy loading and infinite scroll?
- Auditing rendering backwards: from rendered page to rendering tree
- Which AI crawlers actually render JavaScript — and why it changes per fetch
- Serving Markdown via the Accept header vs. .md URLs vs. llms.txt
- Why bad ARIA labels make AI agents take the wrong action on your site
A masterclass in the infrastructure layer of search visibility — what machines can actually access, interpret, and act on.
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💬 Giacomo serves Markdown to any bot that asks for it — Google's advice notwithstanding. Would you serve Markdown to AI crawlers on a client site, or is HTML-only still the right call? Tell us in the comments.
Connect with Giacomo Zecchini✅ Follow Giacomo Zecchini on LinkedIn: https://www.linkedin.com/in/gzecchini/✅ Follow Giacomo Zecchini on X / Twitter: https://x.com/giacomozecchini✅ Follow Giacomo Zecchini on Bluesky: https://bsky.app/profile/giacomozecchini.bsky.social✅ Follow Giacomo Zecchini on Mastodon: https://mastodon.social/@giacomozecchini✅ Follow Giacomo Zecchini on SpeakerDeck: https://speakerdeck.com/giacomozecchini✅ Follow Giacomo Zecchini on SlideShare: https://www.slideshare.net/giacomozecchini✅ Giacomo Zecchini's Personal Website: https://giacomozecchini.com
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🛠️ Tools & Resources Mentioned• Merj Official Site: https://merj.com• Google JS Rendering Capabilities Research with Vercel: https://vercel.com/blog/how-google-handles-javascript-throughout-the-indexing-process• AI Cralwer's Accept Language Research: https://www.linkedin.com/posts/merj-com_this-is-something-most-multilingual-sites-activity-7434943896385822720-T2u1• Merj's take on serving Markdown Files: https://www.linkedin.com/posts/merj-com_ai-agents-are-reading-your-site-right-now-activity-7466111771209142272-3xEy
