How do you check SEO after a website migration?

Last updated: 23 October 2026

Check SEO after a website migration by comparing, page by page, the fields search engines read on the old site and the new one: the title, H1, meta description, canonical, robots meta tag, hreflang links and body text. A changed title or a lost description can cost rankings, and a canonical left on the old host or a stray noindex can remove a page from results altogether.

Check it by hand

Start from a list of page pairs: each old URL and the new URL it moves to. The website migration testing checklist explains how to build that list, and finding broken pages after a migration makes sure every pair answers 200 before you compare it. Then, for each pair, open the page source on both sites and compare:

Title. The <title> should match, or change only where you meant it to. Templates often drop the page name and leave only the brand.
H1. The main heading should carry the same words. A theme that turns the H1 into a styled <div>, or that adds a second H1 for the logo, changes what search engines read as the page topic.
Meta description. Importers often skip it, and an empty description lets the search engine pick its own snippet.
Canonical. The <link rel="canonical"> should point at the page’s own new address. A canonical that still names the old host tells search engines to keep the old URL, which after the switch redirects or no longer exists.
Robots meta tag. Look for noindex or none carried over from staging. A page with no robots tag is treated as index, follow.
Hreflang. On a multilingual site, each language version should list the same languages, each pointing at the matching page on the new site.
Body text. Compare the words on the page, not only the headings. Missing blocks, collapsed tabs and truncated imports remove content search engines used to rank the page.

Then confirm that the new sitemap.xml lists the new URLs and that the new robots.txt does not block the site.

What DiffiCat automates

DiffiCat runs this comparison as “Content”, one of its three checks, on every page pair it finds. Each field is compared between Site A, the site you are moving from, and Site B, the site you are moving to:

Title, H1 and meta description are compared as text, and any difference is flagged.
Canonical is compared by path, so a canonical that moves from old.example/pricing to new.example/pricing passes. A canonical on the new site that still names the old site’s host is flagged.
Robots meta is compared after normalisation: the directives are lower-cased, deduplicated and sorted, and a missing tag counts as index, follow. A page that gains noindex or none on the new site is flagged at high severity.
Hreflang is compared as a set of language and path pairs, so a change of host or order passes and a missing language or a changed path fails.
Body text fails when fewer than 90% of the words overlap. The report then shows the words added and removed and the passages that changed.

The same run also checks that every page exists and compares screenshots, at 375 px, 768 px or 1440 px, or any width from 320 px to 2560 px.

What this does not catch

Other headings. DiffiCat compares the H1 only; H2 to H6 changes show up only through the body text.
Structured data, image alt text, internal links and Open Graph tags are not compared field by field.
Rankings themselves. A page can match exactly and still drop while search engines recrawl; watch your search console for several weeks after launch.

DiffiCat has its own limits. Both sites must resolve on the public internet: localhost, loopback and private-network addresses are refused, so deploy staging to a public URL (password protection is fine). Pages are rendered in headless Chromium only. Sign-ins that need a code (MFA), a CAPTCHA or single sign-on are not supported.

Check the SEO of your migration

Enter your old and new site in the try-it form, or open app.difficat.com and start the free trial: 500 captured pages once when signed in, 100 without signing in, with every check and no card needed.