Free SEO Tool

Ostr.io Prerendering Checker

Verify that your website has ostr.io pre-rendering properly configured. We'll request your page as Googlebot and check for thex-prerender-idresponse header.

Why Prerendering Matters for JavaScript Websites

Modern web applications built with frameworks like React, Angular, Vue, and Next.js often rely on client-side JavaScript to render content. While this creates great user experiences, it poses a significant challenge for search engines and AI crawlers: many bots cannot execute JavaScript, which means they see blank or incomplete pages.

Prerendering solves this by generating fully rendered HTML snapshots of your pages and serving them to crawlers. The ostr.io pre-rendering service handles this automatically — no code changes required.

How to Verify Your Setup

When ostr.io pre-rendering is active, every response served to a crawler includes the x-prerender-id header. This tool automates the verification process:

  1. Enter your page URL above
  2. We fetch the page using Googlebot's official User-Agent string
  3. We check the response headers for the x-prerender-id field
  4. A green result means pre-rendering is active; red means it needs setup

Benefits of Prerendering

  • Complete indexation — search engines see fully rendered content, not empty JavaScript shells
  • Faster crawling — pre-rendered HTML loads instantly without waiting for JavaScript execution
  • AI visibility — AI crawlers like GPTBot, ClaudeBot, and PerplexityBot get your complete content
  • Social sharing — Open Graph tags and metadata are properly visible to social media crawlers
  • Zero code changes — works at the CDN/proxy level without modifying your application

Frequently Asked Questions

What is pre-rendering and why does it matter?
Prerendering is the process of generating static HTML snapshots of your JavaScript-heavy pages (React, Angular, Vue, etc.) so that search engine crawlers can read and index them properly. Without pre-rendering, bots that don't execute JavaScript may see blank or incomplete pages, which hurts your SEO rankings and visibility.
What is the x-prerender-id header?
The x-prerender-id header is a response header added by ostr.io's pre-rendering service. When present and non-empty, it confirms that the page was served through the pre-rendering pipeline. This tool checks for that header to verify your setup is working correctly.
How does this checker work?
The tool sends an HTTP request to your URL using Googlebot's official User-Agent string. It then inspects the response headers for the x-prerender-id field. If the header is present with a valid value, your pre-rendering is active. If it's missing, the page is not being served through ostr.io's pre-rendering service.
Why does the check use the Googlebot User-Agent?
Prerendering services typically activate only for known search engine crawlers. By fetching the page as Googlebot, we simulate the exact scenario where pre-rendering should be triggered. If the header appears for Googlebot, it will also work for other supported crawlers like Bingbot, YandexBot, and AI bots.
The check shows "Not Detected" — what should I do?
This means the x-prerender-id header was not found in the response. Common causes include: pre-rendering not being set up yet, incorrect middleware or proxy configuration, the URL not matching your pre-rendering rules, or DNS/CDN settings not routing crawler traffic through the pre-rendering service. Visit ostr.io to set up or troubleshoot your configuration.
Can I check any URL or only my own?
You can check any publicly accessible URL. This is useful for verifying your own sites, auditing competitor setups, or confirming that pre-rendering is working across different pages and subdomains of your website.
Is this tool free to use?
Yes, the Ostr.io Prerendering Checker is completely free with no registration required. You can check as many URLs as you need.
What is ostr.io?
Ostr.io is a pre-rendering service that generates and caches fully rendered HTML snapshots of JavaScript-heavy web pages. It serves these snapshots to search engine and AI crawlers, ensuring your SPA or dynamic content is fully visible and indexable — without changing your application code.