XML Sitemap Validator

The limits are hard limits

A sitemap file may contain at most 50,000 URLs and may be at most 50MB uncompressed. Go over either and the whole file is rejected — not truncated, rejected. Split it and list the parts in a sitemap index, which has the same two limits applied to the number of sitemaps it points at.

The 50MB figure is the uncompressed size. Gzipping the file is a good idea for transfer, and it does not raise the ceiling: a 60MB sitemap that gzips to 4MB is still over the limit.

lastmod is the only optional element Google still reads

Google has said plainly that it ignores <changefreq> and <priority> completely. Setting every page to 1.0 does nothing, and neither does setting them honestly. They are not harmful, they are just noise, and a sitemap generator that fills them in is telling you it was written a long time ago.

<lastmod> is different — Google does use it, on one condition: it has to be true. If your CMS stamps today's date on every URL every night, Google notices the dates are meaningless and starts ignoring the element for your whole site. That is worse than omitting it. Use the date the content actually changed, and if you cannot produce that, leave the element out.

What a sitemap can and cannot contain

• Absolute URLs only. /pricing is invalid. It needs the protocol and the host, every time.
• One host per file. Every URL must be on the same host as the sitemap itself, unless you have verified cross-submission in Search Console. Mixing example.com and www.example.com counts as two hosts.
• Properly escaped. A bare & in a URL is a well-formedness error and kills the whole file. It must be &. This is the single most common reason a sitemap parses in a browser but fails in Search Console.
• Only indexable URLs. The file is a list of pages you want indexed. Including URLs that are noindexed, canonicalised elsewhere, redirected or 404ing is not an error in the XML, but it is the fastest way to make the coverage report unreadable.

Why Search Console says "Couldn't fetch"

Nine times out of ten this is not the XML. It is the sitemap URL returning a 404, a 301 to somewhere else, or an HTML page from a CDN error handler. Search Console reports all of those the same way. Fetch the sitemap URL yourself with the cache bypassed before assuming the file is at fault — and check that /robots.txt is not disallowing the path the sitemap lives on, which is a genuinely common own goal.