Knowledge base v2.13.0 · Community edition · data through 2 October 2026
Thing · Standard
The web's scripting language; Google renders JavaScript before indexing, but content and links that need it are at risk.
Documented in
Google's Inside Googlebot post warns that bloated inline base64 images, large blocks of inline CSS or JavaScript, or megabytes of menus can push a page's text or structured data past Googlebot's 2MB cutoff, and advises moving heavy CSS and JavaScript to external files and placing meta tags, the title, the canonical and essential structured data high in the HTML.
Search Central blog (31 March 2026) · Day 1 · How crawling works
Google's robots meta tag specification says data-nosnippet may be extracted both before and after rendering, so the attribute should not be added to or removed from existing elements with JavaScript.
Google Search Central · Day 2 · Controlling indexing
Google's meta tags documentation recommends avoiding JavaScript to inject or change meta tags whenever possible and testing the implementation thoroughly when it must be used.
Google Search Central · Day 2 · Controlling indexing
Google's JavaScript SEO basics guide says that when Google encounters a noindex rule it may skip rendering and JavaScript execution, so using JavaScript to change or remove a noindex robots meta tag may not work as expected.
Google Search Central · Day 2 · Controlling indexing
Google's JavaScript SEO guide says Googlebot sends every page with a 200 HTTP status code to the rendering queue, whether or not it contains JavaScript, unless a robots meta tag or header tells Google not to index it, and Google uses the rendered HTML to index the page.
Google Search Central · Day 2 · Lightning session D: Rendering and JavaScript
Google's JavaScript SEO basics guide says Googlebot extracts links twice, from the HTML response before rendering and again from the rendered HTML, so links injected with JavaScript can be found if they use crawlable <a href> markup.
Google Search Central · Day 2 · Lightning session D: Rendering and JavaScript
Google's JavaScript SEO basics guide says a page may wait in the render queue for a few seconds but that it can take longer, and it gives no upper limit.
Google Search Central · Day 2 · Lightning session D: Rendering and JavaScript
Google's JavaScript guides say that when client-side routing makes a real 404 status impractical, a single-page app can avoid soft 404s by redirecting with JavaScript to a URL whose server returns 404, or by adding a robots noindex meta tag with JavaScript.
Google Search Central · Day 2 · Lightning session D: Rendering and JavaScript
Google says its Web Rendering Service fetches the resources a page references through Googlebot, including JavaScript, CSS and XHR requests to APIs, but not images or videos.
Search Central blog (3 December 2024), Search Central blog (31 March 2026) · Day 2 · Lightning session D: Rendering and JavaScript
Google's JavaScript SEO basics says every page with a 200 status code is queued for rendering, whether or not it uses JavaScript, unless a robots meta tag or header says not to index it; for non-200 pages such as 404 error pages, rendering might be skipped.
Google Search Central · Day 2 · What is Google friendly JavaScript
For effects that need WebGL, which Googlebot does not support, Google's guide to fixing JavaScript problems suggests skipping the effect or prerendering it with server-side rendering so that the content is accessible to Googlebot.
Google Search Central · Day 2 · What is Google friendly JavaScript
Google's JavaScript SEO basics recommends differential serving and polyfills when feature detection finds a missing browser API, and warns that some browser features cannot be polyfilled.
Google Search Central · Day 2 · What is Google friendly JavaScript
For client-side rendered single-page apps, where meaningful status codes can be impossible or impractical, Google's documentation gives two ways to avoid soft 404s: a JavaScript redirect to a URL that returns a 404 status, or a noindex robots meta tag added with JavaScript.
Google Search Central · Day 2 · What is Google friendly JavaScript
Google's guide to fixing Search-related JavaScript problems says its Web Rendering Service keeps no state across page loads: local storage, session storage and HTTP cookies are cleared.
Google Search Central · Day 2 · What is Google friendly JavaScript
Google's guide to fixing Search-related JavaScript problems says the Web Rendering Service may ignore caching headers and so use outdated JavaScript or CSS, and recommends content fingerprinting, which puts a hash of the content in the file name, as in main.2bb85551.js.
Google Search Central · Day 2 · What is Google friendly JavaScript
Slide and stage claims that name it, the ones Google’s documentation does not cover first.
Dave Smart said robots.txt is checked for every URL in a redirect chain and crawling stops at the first blocked one; in his example a site redirected through /cart/ with JavaScript to set the local currency and back, and because /cart/ was disallowed the page was reported as blocked.
Dave Smart · Day 1 · Lightning session B: Robots.txt
Dave Smart said this applies to all redirects, not only JavaScript ones; his examples: a redirect through an external authorisation service that is blocked by its own robots.txt, content that moved through several URLs over the years with one of them later blocked, and unexpected redirects, such as one served only to Googlebot's user agent.
Dave Smart · Day 1 · Lightning session B: Robots.txt
A Google panelist said, as a fun fact, that JavaScript was used for the language-consolidation redirects in Google's own site migration, because it was the only option available to the person doing it (the recording does not make fully clear whether the JavaScript performed the redirects or built the mapping).
Being able to render and read JavaScript matters whether the client fetching a page is a search crawler or an AI system, Google said.
Erin Sparling · Day 2 · Lightning session D: Rendering and JavaScript
Google described the mission of its rendering as simply executing JavaScript, while the implementation is complex, expensive and difficult.
Erin Sparling · Day 2 · Lightning session D: Rendering and JavaScript
Google said its pipeline needs to ensure that content indexable without JavaScript can pass through without rendering, while content that appears only through JavaScript and CSS takes a longer rendering pass.
Erin Sparling · Day 2 · Lightning session D: Rendering and JavaScript
Switching JavaScript off and on in the browser gives a quick first impression of which content on a page depends on rendering.
Sören Bendig · Day 2 · Lightning session D: Rendering and JavaScript
If the cause of missing JavaScript content is still unclear after checking the network requests, search the source code for a string related to the missing content.
Rebecca Yu · Day 2 · Lightning session D: Rendering and JavaScript
Natalia Venditto named three typical failure modes by which an embedded app can break the application hosting it: collisions in the global JavaScript scope and module registry, CSS bleed, and fate sharing.
Natalia Venditto · Day 2 · Lightning session D: Rendering and JavaScript
An iframe, the long-established way to embed an app, isolates both JavaScript and styles but is not part of the page: it is walled off from the host's DOM, navigation and layout, which Natalia Venditto said brings many problems with accessibility, layout and navigation.
Natalia Venditto · Day 2 · Lightning session D: Rendering and JavaScript
Shadow DOM isolates styles and keeps the embedded content part of the page, but it does not isolate JavaScript: the embedded code still shares the host's JavaScript globals.
Natalia Venditto · Day 2 · Lightning session D: Rendering and JavaScript
Rewriting everything into one application keeps the result part of the page, but JavaScript and style isolation then have to be done by hand.
Natalia Venditto · Day 2 · Lightning session D: Rendering and JavaScript
Reframing with Web Fragments was the only approach on the comparison slide ticked for all three criteria (JavaScript isolated, styles isolated, part of the page); its stated catch is that it relies on browser patches today.
Natalia Venditto · Day 2 · Lightning session D: Rendering and JavaScript
Web Fragments is a lightweight library that puts a hidden iframe in the host page and uses it as an isolated sandbox to run the embedded app's JavaScript, not to render the app.
Natalia Venditto · Day 2 · Lightning session D: Rendering and JavaScript
Web Fragments reframes the embedded app's DOM by placing it inside a shadow DOM in the host page, while the app's JavaScript runs in the hidden iframe.
Natalia Venditto · Day 2 · Lightning session D: Rendering and JavaScript
Natalia Venditto said Web Fragments is framework-agnostic and vendor-agnostic and works the same whatever JavaScript framework the embedded app uses.
Natalia Venditto · Day 2 · Lightning session D: Rendering and JavaScript
Natalia Venditto said ShadowRealm, a JavaScript standard proposal, was at stage 2.7 at the time of the talk, which she glossed as meaning that only implementation is missing.
Natalia Venditto · Day 2 · Lightning session D: Rendering and JavaScript
Google's slide called content missing from the rendered HTML the most common JavaScript issue for indexing.
Erin Sparling · Day 2 · What is Google friendly JavaScript
Erin Sparling called URL fragments (the part of a URL after #) the next most common JavaScript issue seen, after rendering problems and blocked rendering.
Erin Sparling · Day 2 · What is Google friendly JavaScript
Version 20 of the Screaming Frog SEO Spider, released in May 2024, was the first that could connect the crawler to ChatGPT through custom JavaScript, which let SEOs rewrite image alt text at scale.
To test LLM-generated alt text before a rollout, a community speaker recommended running the crawler's custom JavaScript in Screaming Frog's List mode on a few chosen URLs and reviewing the generated alt text, instead of crawling the whole site in Spider mode.
A community speaker advised against publishing markdown copies of HTML pages for AI agents: the copy is a duplicate (which the speaker also called a possible source of cloaking, an uncertain word in the recordings), and the models are trained to read HTML, CSS and JavaScript.
Carlos Ortega · Day 1 · Lightning session A: Automation and AI
Google cannot extract a link from an a element that only has an onclick handler, because Googlebot does not click, so the JavaScript is never triggered.
A slide said robots meta rules can be added to a page's HTML with JavaScript, but doing so takes more time.
John Mueller · Day 2 · Controlling indexing
Removing a robots restriction such as noindex with JavaScript does not work, a slide said.
John Mueller · Day 2 · Controlling indexing
When Google finds a noindex rule in a page's HTML, it drops the page without even processing its JavaScript, so a script cannot switch the page back to indexable, John Mueller said.
John Mueller · Day 2 · Controlling indexing
Without its ability to render JavaScript, Google says it would not be able to see most of what is on the web today.
Erin Sparling · Day 2 · Lightning session D: Rendering and JavaScript
A Google pipeline diagram ran from the crawl queue to the crawler, then through HTML parsing to processing, which passes pages to rendering and gets them back, and then to the index; rendering fetches its JavaScript and CSS through the crawler.
Erin Sparling · Day 2 · Lightning session D: Rendering and JavaScript
Google urged sites to make sure their JavaScript content can be crawled, rendered and indexed, calling this important today and also tomorrow, as AI systems increasingly ground answers to user requests.
Erin Sparling · Day 2 · Lightning session D: Rendering and JavaScript
A community speaker strongly advised putting everything you want cited into the raw, server-side rendered HTML, especially for AI systems that cannot render JavaScript yet.
Sören Bendig · Day 2 · Lightning session D: Rendering and JavaScript
In a navigation example, the main navigation was in the raw HTML and would survive a rendering failure, but the whole sub-navigation was built by JavaScript, so all of its links would be inaccessible to bots if rendering broke.
Sören Bendig · Day 2 · Lightning session D: Rendering and JavaScript
If JavaScript rendering fails, what Google indexes for a page differs from what the page shows once it is rendered.
Erin Sparling · Day 2 · What is Google friendly JavaScript
Erin Sparling named server-side or hybrid rendering, fallbacks and not leaving placeholders in the DOM, among other measures, as ways to guard against failed JavaScript rendering.
Erin Sparling · Day 2 · What is Google friendly JavaScript
Google listed four common JavaScript problems for indexing: content not present in the rendered HTML, using # in URLs for content changes, soft 404s and blocked resources.
Erin Sparling · Day 2 · What is Google friendly JavaScript
Blocked resources, one of Google's four common JavaScript indexing problems, means robots.txt disallowing the crawling of critical JavaScript files or API endpoints.
Erin Sparling · Day 2 · What is Google friendly JavaScript
Google named three causes of content missing from the rendered HTML: JavaScript inaccessible to Googlebot, JavaScript DOM event triggers and disabled browser APIs.
Erin Sparling · Day 2 · What is Google friendly JavaScript
When the JavaScript is not accessible to Googlebot, Google cannot render the client-side DOM that the page builds asynchronously, so parts of the page may be present while the main content is absent.
Erin Sparling · Day 2 · What is Google friendly JavaScript
Whether a page can load is really important for canonical selection: a broken certificate, failing JavaScript or a page that cannot be loaded counts against a URL, and the slide also listed meta refresh and security.
Content that JavaScript adds to a page is typically seen by Google's indexing system within a few hours, and at worst within weeks.
Gary Illyes · Day 3 · How long does it take to..?
Google renders JavaScript-heavy pages from their HTML, CSS and JavaScript as a browser would, using the latest version of Chromium.
Cherry Prommawin · Day 1 · How Search works and where's AI?
A community speaker said AI agents understand a page through a combination of three inputs: a screenshot, the DOM (the HTML plus the changes rendered by JavaScript) and the accessibility tree.
Carlos Ortega · Day 1 · Lightning session A: Automation and AI
John Mueller recommended putting robots meta tags directly in a page's HTML exactly as intended, and adding them with JavaScript only where that is not possible, as in a JavaScript web app.
John Mueller · Day 2 · Controlling indexing
The diagram from Google's JavaScript SEO basics page shows a URL going from the crawl queue to the crawler, the crawled HTML going to processing, then the render queue and the renderer, whose rendered HTML returns to processing before the page reaches the index.
Rebecca Yu · Day 2 · Lightning session D: Rendering and JavaScript
Google's renderer is a headless Chromium that runs the page's JavaScript.
Rebecca Yu · Day 2 · Lightning session D: Rendering and JavaScript
To check whether JavaScript content is affected, open the URL Inspection tool in Search Console or the Rich Results Test and look for that content in the rendered HTML tab.
Rebecca Yu · Day 2 · Lightning session D: Rendering and JavaScript
Blocking JavaScript or API resources in robots.txt is a classic rendering mistake: if Google's renderer cannot fetch a resource, it cannot run it.
Rebecca Yu · Day 2 · Lightning session D: Rendering and JavaScript
Google's slide defined a soft 404 in a JavaScript application as a page that serves a 'Not Found' message but returns a 200 HTTP status code.
Erin Sparling · Day 2 · What is Google friendly JavaScript
In JavaScript single-page apps, soft 404s typically arise because the server returns the app with a 200 status for every URL, so when the app shows a 'not found' message for a URL that does not exist, no error is reported.
Erin Sparling · Day 2 · What is Google friendly JavaScript
If robots.txt blocks JavaScript that client-side code needs to render, Google cannot render the content that the JavaScript would produce.
Erin Sparling · Day 2 · What is Google friendly JavaScript
An audience member asked what happens to thousands of crawled and indexed paginated category and tag pages if they are replaced by a single page with a JavaScript load-more button, and whether the old pages should then redirect to the canonical first page.
From the audience · Day 1 · Q&A
Google framed rendering historically: when Google started, most of the web was plain, semantic HTML it could extract directly, but the modern web is built with JavaScript and much content is generated by JavaScript, so Google had to adapt.
Erin Sparling · Day 2 · Lightning session D: Rendering and JavaScript
After Google's opener, Lightning session D had three community talks: rendering and JavaScript execution blind spots (Sören Bendig), debugging JavaScript rendering for Search (Rebecca Yu) and virtualizing the browser (Natalia Venditto).
Erin Sparling · Day 2 · Lightning session D: Rendering and JavaScript
Because even established brands have these rendering problems and every modern website uses a lot of JavaScript, a community speaker argued that most sites probably have them too and that ignoring rendering is reckless.
Sören Bendig · Day 2 · Lightning session D: Rendering and JavaScript
The second community lightning talk of the rendering block covered debugging JavaScript rendering for Search: how Google renders pages, a step-by-step check, four common mistakes and a worked product page example.
Rebecca Yu · Day 2 · Lightning session D: Rendering and JavaScript
A community speaker listed four common but often overlooked JavaScript rendering mistakes: non-crawlable link markup, error pages that return HTTP 200 in single-page apps, content behind user interaction, and JavaScript or API resources blocked in robots.txt.
Rebecca Yu · Day 2 · Lightning session D: Rendering and JavaScript
A community speaker called not hiding content behind user interaction the most important of the four JavaScript rendering mistakes.
Rebecca Yu · Day 2 · Lightning session D: Rendering and JavaScript
A community speaker summed up JavaScript rendering issues as cases where search engines cannot execute, access or trigger the code needed to display a page's core content.
Rebecca Yu · Day 2 · Lightning session D: Rendering and JavaScript
Natalia Venditto, a Principal Software Engineer at Adobe, gave a seven-minute community lightning talk on JavaScript and web standards, built around the Web Fragments library.
Natalia Venditto · Day 2 · Lightning session D: Rendering and JavaScript
A slide titled Orchestration approaches compared four ways to combine micro-frontends in one page (iframe, Shadow DOM, rewriting everything, and reframing with Web Fragments) on three criteria (JavaScript isolated, styles isolated, part of the page) and named the catch of each.
Natalia Venditto · Day 2 · Lightning session D: Rendering and JavaScript
Websites that rely heavily on JavaScript and rendering have common blind spots, because these features often break in subtle ways, a community speaker said.
Sören Bendig · Day 2 · Lightning session D: Rendering and JavaScript
Google's redirects guide says Google Search follows JavaScript location redirects only after rendering, may never see one if rendering fails, and should be used only when server-side or meta refresh redirects are impossible; its site move guide asks for server-side permanent redirects (301 or 308) where technically possible. The JavaScript in Google's own migration was a fallback ('my only option'), not a pattern to copy.
Ibrahim Anjro · Day 1 · Q&A
Audit every template and JavaScript component that outputs links, such as navigation, pagination, filters and product tiles: each needs a real a element with an href, because onclick handlers, routerLink without href, href on a span and javascript: URLs leave the target pages without a link Google can reliably extract.
Ibrahim Anjro · Day 2 · How is HTML interpreted
Ship robots rules in the HTML the server sends and never rely on JavaScript to lift a noindex: Google may skip rendering a page that arrives with noindex, so the page can stay out of the index even if a script removes the tag later.
Ibrahim Anjro · Day 2 · Controlling indexing
On stage the rule was absolute (Google won't even process the JavaScript of a page served with noindex), while Google's guide says only that it may skip rendering; either way, a noindex in the served HTML must never be one that JavaScript is expected to lift.
Ibrahim Anjro · Day 2 · Controlling indexing
For pages people are likely to ask an AI assistant about (product, pricing, documentation and policy pages), server-render the main content so a live, user-triggered read does not depend on client-side JavaScript finishing quickly.
Ibrahim Anjro · Day 2 · Lightning session D: Rendering and JavaScript
The stage remark that content indexable without JavaScript can pass through without rendering does not mean such pages skip rendering, because Google's guide queues every 200 page for rendering; read it as: content already in the raw HTML does not depend on the slower rendering pass.
Ibrahim Anjro · Day 2 · Lightning session D: Rendering and JavaScript
Put everything indexing depends on (title, meta description, canonical, robots meta tag, main text and links) in the raw HTML so it is available without rendering, let JavaScript add enhancements only, and check the rendered HTML in URL Inspection for the rest.
Ibrahim Anjro · Day 2 · Lightning session D: Rendering and JavaScript
When something is missing from a rendered page, check both robots.txt and the Content Security Policy: the URL Inspection live test shows the page resources, the JavaScript console output and a screenshot of the rendered page.
Ibrahim Anjro · Day 2 · Lightning session D: Rendering and JavaScript
In a single-page app, let the server return 404 for unknown routes where possible; otherwise use one of the two client-side fixes Google documents for error views: a JavaScript redirect to a URL that returns 404, or a robots noindex added with JavaScript.
Ibrahim Anjro · Day 2 · Lightning session D: Rendering and JavaScript
Pages that embed third-party or AI-generated apps can share their fate, since an unhandled exception in the embedded code can break the host page; check the rendered HTML and JavaScript console output of such pages in Google's testing tools to make sure the host's own content still renders.
Ibrahim Anjro · Day 2 · Lightning session D: Rendering and JavaScript
Make sure robots.txt does not block the URLs from which the browser loads a fragment's assets (the gateway paths on the host page's origin, or the endpoint's own host if assets load from there), because Google does not render JavaScript from blocked files and robots.txt rules apply per host.
Ibrahim Anjro · Day 2 · Lightning session D: Rendering and JavaScript
Check robots.txt for Disallow rules covering JavaScript bundles, build folders or API endpoints the page calls while rendering, including on separate API or CDN hostnames with their own robots.txt, then confirm in URL Inspection's live test that the rendered HTML contains the main content.
Ibrahim Anjro · Day 2 · What is Google friendly JavaScript
Put critical content, links and meta tags in the server HTML: content that needs JavaScript reaches indexing only after rendering, usually within hours but sometimes weeks, and even Google's own speaker doubted that every URL gets rendered.
Ibrahim Anjro · Day 3 · How long does it take to..?
The stage doubt that every URL gets rendered sits beside Google's JavaScript guide, which says every page with a 200 status is queued for rendering unless a robots rule blocks indexing: queued is not the same as rendered, so do not rely on rendering for critical content.
Ibrahim Anjro · Day 3 · How long does it take to..?
Kit items about JavaScript: their own words name it, or several of the claims they rest on do.
Do not add, change or remove robots meta tags with JavaScript
Rests on 9 claims, 9 of them naming JavaScript; its own words name JavaScript
Server-render the main content and everything indexing depends on (SSR, static generation or hybrid)
Rests on 11 claims, 7 of them naming JavaScript; its own words name JavaScript
Return a real 404 for unknown routes in single-page apps, or use a documented client-side fallback
Rests on 7 claims, 4 of them naming JavaScript; its own words name JavaScript
Do not block JavaScript, CSS or API endpoints that pages need for rendering in robots.txt
Rests on 7 claims, 4 of them naming JavaScript; its own words name JavaScript
Make rendering robust: no slow API dependencies and no unresolved placeholders
Rests on 8 claims, 3 of them naming JavaScript
Use permanent server-side redirects (301 or 308) for moved URLs, straight to the final URL
Rests on 10 claims, 2 of them naming JavaScript; its own words name JavaScript
Never route a crawlable URL's redirects through a URL that robots.txt blocks
Rests on 4 claims, 2 of them naming JavaScript; its own words name JavaScript
Rests on 7 claims, 2 of them naming JavaScript; its own words name JavaScript
Make JavaScript-generated content render quickly
Rests on 5 claims, 2 of them naming JavaScript; its own words name JavaScript
Feature-detect permission-based APIs and WebGL, and render the content without them
Rests on 5 claims, 2 of them naming JavaScript
Monitor JavaScript console errors and Content Security Policy violations on key templates
Rests on 4 claims, 2 of them naming JavaScript; its own words name JavaScript
Serve one host over HTTPS with a valid certificate and redirect every other origin to it
Rests on 4 claims, 1 of them naming JavaScript; its own words name JavaScript
Keep each HTML response well under 2 MB and put the main content and JSON-LD early
Rests on 2 claims, 1 of them naming JavaScript; its own words name JavaScript
Have all indexable content in the DOM after load, without clicks, typing or scrolling
Rests on 8 claims, 1 of them naming JavaScript; its own words name JavaScript
Make every navigational link an <a> element whose href holds a real URL
Rests on 6 claims, 1 of them naming JavaScript; its own words name JavaScript
Try WebMCP to declare the actions a site offers to AI agents
Rests on 4 claims, 0 of them naming JavaScript; its own words name JavaScript
List important images in an image sitemap
Rests on 2 claims, 0 of them naming JavaScript; its own words name JavaScript
Also inglossary terms Raw HTML and rendered HTML, Rendering, Shadow DOM, Single-page app (SPA), URL Inspection tool
Things named in the same claim, with the number of claims they share.