I check this on nearly every technical audit now, and I want to explain why it's such a common, easy-to-miss gap, since it doesn't show up as an obvious error the way a broken link does.
Why This Gap Exists in the First Place
Googlebot's JavaScript rendering, while imperfect, has had years of dedicated engineering investment and a two-wave crawl-and-render process specifically built to handle it. AI crawlers are newer, generally simpler, and built primarily around efficiently fetching large volumes of raw content for training or retrieval, not necessarily replicating a full browser rendering environment for every page. Some AI crawlers reportedly can render JavaScript to varying degrees, but the reliability and consistency doesn't match what Googlebot has built up, and for several major AI crawlers, JavaScript execution isn't part of the fetch process at all.
What This Actually Looks Like on a Real Site
Which HTTP status code should be used for a permanent URL redirect?
If your site's core content, service descriptions, blog posts, key value propositions, only appears after JavaScript executes, a single-page application, or a site heavily reliant on client-side rendering for its main content, an AI crawler fetching the raw HTML may see an essentially empty page, just a loading shell with no actual content for it to read, extract, or cite. The site can look completely normal to a human visitor, and even rank reasonably in classic Google search, while being functionally blank to a crawler that doesn't execute the JavaScript building that content.
How to Actually Check This Yourself
The simplest test: disable JavaScript in your browser, or use a browser's developer tools to view the page's raw, unrendered HTML source, and see what content is actually present without JavaScript execution. If your core content disappears entirely in that view, that's very likely close to what a non-rendering AI crawler sees when it fetches your page. This is a genuinely quick check anyone can run without specialized tools, and I'm always a little surprised by how few site owners have actually looked.
What an AI crawler sees vs. what a human sees on a JS-heavy page
The Fix, at a Technical Level
The most reliable fix is server-side rendering (SSR) or static site generation for core content, ensuring the meaningful text and structure exist in the initial HTML response, before any JavaScript runs, rather than depending entirely on client-side rendering to construct it. This doesn't mean abandoning JavaScript-driven interactivity entirely, it means making sure the core, citable content, the actual substance a crawler or a human would want to read, isn't locked behind a rendering step some crawlers simply skip.
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Why This Connects Directly to AI-Search Visibility Specifically
This is exactly the kind of issue that can silently undermine AI-search visibility work happening everywhere else on a site. You can build excellent entity architecture, comprehensive topical content, and clean schema, and still get zero AI citation if the underlying content never actually reaches the crawler in the first place. This is part of why checking this specifically is standard on every audit I run, not an optional, advanced-tier check, and it connects directly to the passage-retrieval mechanics covered in how ChatGPT Search actually sources content, a crawler can't retrieve a passage it never received in the first place.