Hreflang is where I see the most silent mistakes, and the hreflang tags testing tool on technicalseo.com (by Merkle) is what I use to check pages before and after launch.
My routine:
– Test the URL and look for missing return tags. If the German page points to the French page but not back, Google may ignore the pair.
– Check that every alternate URL returns 200 and is not redirected or canonicalised somewhere else. The tool shows status codes for each.
– Confirm language and region codes are valid. en-UK instead of en-GB still shows up surprisingly often.
– Use the generator on the same site to build sitemap hreflang for sites with many locales.
Downside: it checks one URL at a time, so it is for spot checks. For a full site audit you still need a crawler that validates hreflang across all pages.
https://technicalseo.com/
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