Pre-rendering Tester
Compare a live URL's raw HTML against its JavaScript-rendered version — an SEO-signal table (title, meta description, canonical, H1s, word count, links) plus a full markup diff, so you can see exactly what only shows up after JS runs.
Input
Fetched and rendered server-side through a real headless browser — takes a few seconds longer than a plain fetch.
Result
The SEO-signal comparison and HTML diff will appear here.
Guides
What Pre-rendering Tester does
Enter a live URL and this tool fetches its raw HTML (a plain request, no JavaScript) and its fully rendered DOM (through a real headless Chromium browser), then compares them two ways: an SEO signals table covering the fields that actually matter for indexing — title, meta description, canonical URL, H1 count, word count, and link count — and a full line-level HTML diff underneath showing every markup change JavaScript made.
How to use it
- Enter the full URL of the page you want to check.
- Click Test pre-rendering. The page is fetched and rendered on our server, which takes a few seconds longer than a plain fetch.
- Check the SEO Signals table first — any row marked as a mismatch means that signal only exists (or differs) after JavaScript runs. Scroll into the HTML Diff for the full picture: green lines only exist in the rendered version, red lines only exist in the raw HTML.
Why this matters
A mismatch here doesn't automatically mean a problem — plenty of JS-driven differences (a hydrated header, a lazy-loaded widget) are harmless. What's worth acting on is a mismatch in something crawlers weight heavily and might not wait around for: the <title>, meta description, canonical tag, or H1 changing (or only existing) after render is the classic signature of a client-side-rendered SEO regression.
Scope
The HTML diff is a literal markup comparison, not a semantic one — a page that reformats or reorders otherwise-identical markup between the two fetches will show diff noise unrelated to any real content change. Treat the SEO Signals table as the primary read and the diff as the detail view underneath it, same as recommended for the sibling Fetch & Render tool, which shows the two full documents rather than a diff.
Privacy
The URL is fetched and rendered by our server only to produce this comparison, and isn't stored beyond the job's lifetime. Requests to private or local network addresses are blocked.