Can a clear error message really save your crawl budget from clustering disasters?

What exactly is the unwanted clustering that Allan Scott mentions?

The clustering is how Google groups similar URLs to determine which one to prioritize for indexing. Normally, this mechanism is useful: it prevents duplication and concentrates equity on the best version of a page.

Except that on some JavaScript sites, Google can confuse a real page with an error page. If your 404 returns an HTTP 200 code (soft 404) and displays generic content without an explicit error message, the bot might treat it as a legitimate page. The result? It competes with your real pages within the same cluster, diluting their visibility.

Why are JavaScript sites particularly at risk?

Many JavaScript frameworks (React, Vue, Angular in SPA mode) render everything on the client side. The server always returns a 200 code, even for a non-existent URL, and it's the JavaScript that displays the error message afterward.

Google crawls the raw HTML first, then executes the JS. If nothing in the initial HTML signals the error, the bot might temporarily index the page — or worse, consider it as valid content before even executing the JavaScript. Hence the importance of a textual error message visible right from the initial render.

What are the concrete risks of this clustering?

• Error pages indexed instead of your real pages
• A crawl budget wasted on unnecessary URLs
• Quality signals diluted: if Google sees lots of nearly-empty pages, it might lower the trust level granted to your site
• Canonicals or aberrant automatic consolidations in Search Console

Is this recommendation consistent with real-world observations?

Absolutely. We regularly observe SPA sites with hundreds of soft 404s indexed, often because server-side rendering (SSR) or pre-rendering isn't configured. Google eventually discovers them, but it takes time — and meanwhile, your crawl budget goes up in smoke.

The mention of an "explicit message" confirms what we already knew: Google analyzes textual content to detect errors, not just HTTP codes. A simple "404" or "Page not found" hardcoded into the HTML can be enough to trigger detection, even if the server returned a 200.

What nuances should we add?

Allan Scott speaks of sites "unable to send HTTP status codes". Let's be honest: that's rare. Even with full client-side rendering, solutions exist (SSR, pre-rendering, edge functions, custom headers). If you can return a true 404, do it — it's always more reliable than a textual message.

Next, the message must be explicit. A simple "Oops, something went wrong" might not be enough. Favor clear formulations: "Error 404", "This page does not exist", "Page not found". [To verify]: Google has never published the exact list of text patterns it recognizes as errors. We know it detects "404" and "not found", but beyond that, it's reverse engineering.

In which cases does this rule not apply?

If your site uses server-side rendering (Next.js, Nuxt, SvelteKit with SSR enabled), you can already send a clean HTTP 404 code. Same for static sites or traditional CMS — the issue is almost non-existent.

However, if you have a React/Vue front-end running entirely on the client side, without pre-rendering or SSR, then yes — displaying an explicit error message becomes crucial. But at that point, you probably have deeper SEO problems to solve.

What exactly should you do on a JavaScript site?

First step: audit your error pages. Go to Search Console, "Pages" section > "Excluded", look for soft 404s. If you find many, it means Google isn't detecting your errors correctly.

Next, check the rendering of these pages using Search Console's "URL Inspection" tool. Look at the screenshot: if nothing clearly indicates "404" or "Page not found", add this message directly into the initial HTML, before even JavaScript execution.

How do you implement an explicit error message in JavaScript?

In your error page component (e.g., 404.jsx in React), include a clear and visible text right from the first render. Something like:

<h1>Error 404 – Page not found</h1>

If you use a framework with SSR (Next.js, Nuxt), also configure a 404 HTTP code server-side. In Next.js, it's automatic if you use pages/404.js. In Nuxt, define error.vue with statusCode: 404.

What mistakes should you absolutely avoid?

• Never return a 200 code on an error page if you can avoid it
• Don't settle for a generic message ("Oops", "Something went wrong") — be explicit
• Don't forget to remove error pages from your XML sitemap and internal linking
• Don't block indexing via robots.txt or noindex on 404s — Google needs to crawl them to detect them
• Verify that the error message is present in the source HTML, not just injected by JS afterward