Empirical research on what JavaScript content patterns deliver to bots and LLM fetchers in 2026. Open methodology, open data, reproducible findings.
Status: Phase 1 in progress. First findings expected June 2026.
Eight JavaScript content patterns × five page types × three rendering modes, crawled by all major bot classes. Per-cell signals captured in a public tracker.
Live test bed: next.jsseo.dev — 55 cells running now.
Raw bot tracker data, hypothesis pre-registration, methodology — all open from day one. CC0 / CC-BY for data, MIT for code.
Senior technical SEO consultant, 25 years in the field. Independent owner of SAWA PROJEKT, co-founder of FratreSEO.
Since April 2026 Anthropic's Help Center has linked a crawler IP list at claude.com/crawling/bots.json. I checked ClaudeBot against the wrong Anthropic page, concluded no crawler list existed, and rep...
Across 871 requests, ClaudeBot spent 80% on /robots.txt and /sitemap.xml and 18% on content. The shape explains it: it swept the test bed once through 2026-07-05, then switched to a machine-regular he...
Our JS-execution beacon fires through two channels - an inline script and a React client component. Over 80 days the bots sort into four tiers: renderers that evaluate React but skip inline scripts (A...
We flagged most of our Perplexity and ChatGPT crawler traffic as spoofed. Then we checked whether that was our mistake. It was not. The entire apparent Perplexity, ChatGPT-User and OpenAI-search 'craw...
In 15 days of JS SEO Lab data, the Next.js test bed saw 6,125 hits across 25 user-agent classes. GPTBot, Meta-external, Amazonbot, and three Google sub-bots together produced 862 hits with zero reques...
In the first eight days of JS SEO Lab data, Bingbot fetched our test bed 126 times. 110 of those hits never executed JavaScript. The other 16 — using a different user-agent string — ran the full React...
Vercel and MERJ established in 2024 that batch AI crawlers don't execute JavaScript. That's the rendering-mode answer. But real client audits don't ask "is this site SSR or CSR?" — they ask "is this specific JS pattern (a click-to-reveal, a useEffect-fetched price, a hash-routed navigation) costing me visibility in this specific bot's index?"
Eight JS content patterns (clean / js-images / js-links / click-reveal / js-fetched / hash-routing / late-loaded / mixed) × five page types × three rendering modes (SSR / CSR / optional SSG). Crawled by 25+ bot classes including GPTBot, ChatGPT-User, Claude-User, ClaudeBot, Googlebot, Bingbot, PerplexityBot.
Three-layer bot identification: reverse DNS for Google/Bing/Apple, IP-range CIDR matching against OpenAI/Perplexity published manifests, and explicit unresolved status for bot families without a reliable public verification path, including current Anthropic crawlers. False-positive UAs (deprecated anthropic-ai/Claude-Web) automatically flagged as unverified.