Bad sitemap URLs on platform switchers, by new platform (12-URL-per-site subsample)
| New platform | URLs with known outcome | Bad | Redirect | Canonical elsewhere | Noindex |
|---|---|---|---|---|---|
| Next.js | 1,284 | 15.2% | 8.4% | 3.9% | 1.7% |
| WooCommerce | 824 | 7.6% | 4.0% | 3.0% | 0.4% |
| WordPress | 950 | 5.3% | 3.4% | 0.3% | 1.2% |
| Other platforms | 743 | 16.7% | 7.8% | 5.9% | 1.5% |
| All | 3,801 | 11.4% | 6.1% | 3.2% | 1.2% |
Source: PageSpeed Matters, Oct 2026. Bad includes redirects, canonical elsewhere, noindex and errors; canonical and noindex checked on up to 12 URLs per site.
Summary
An XML sitemap should list only URLs you want indexed: live pages that return a 200, point their canonical at themselves and allow indexing. After a platform switch, sitemaps are often generated fresh by the new system, and they can fill up with URLs that redirect, error or point elsewhere.
We sampled sitemap URLs on 361 sites that changed platform. Counting redirects and client errors, 7.3% of sampled URLs are bad, against 4.3% on 219 comparison sites, a 1.7x gap. Adding canonical and noindex checks on a subsample, 11.4% of listed URLs should not be in the sitemap.
What we measured
We took a random sample of 599 sites in the HTTP Archive crawl of the top 1M sites that switched platform between September 2024 and September 2026. 367 of them had a sitemap with listed URLs we could find. In October 2026 we requested a random sample of listed URLs from each, without following redirects. 361 sites returned answers, giving 10,062 checked URLs.
A URL counts as bad when it redirects or returns a 404, 410 or other client error. Canonical and noindex were checked only on a subsample of 12 URLs per site, 3,801 URLs with a known outcome. The 1.7x comparison covers redirects and client errors only, against 5,266 URLs on 219 full-crawl comparison sites. This is a short study, so treat the results as indicative.
Switcher sitemaps carry more bad URLs, mostly redirects
On redirects and client errors, 7.3% of sampled sitemap URLs on switchers are bad, against 4.3% on the comparison sites. With canonical and noindex checks added on the subsample, 11.4% of listed URLs should not be there: 6.1% redirect, 3.2% canonicalize elsewhere, 1.2% are noindexed and 0.8% return an error.
Redirects are the biggest problem. 6.4% of the 10,062 checked sitemap URLs on switchers redirect, and about a third of those (2.0% of all sampled URLs) only add or drop a trailing slash. That usually means the sitemap and the site disagree on URL format, which is often a single setting.
The problem is concentrated. 70.3% of 313 switchers with 8 or more known URLs had no bad URL in the sample, while 18.8% had 10% or more bad. Of the platforms we can name, sites that moved to Next.js have the dirtiest sitemaps: 15.2% of 1,284 checked URLs are bad and 25.5% of 106 sites have 10% or more bad, against 5.3% of 950 URLs and 11.5% of 78 sites for those that moved to WordPress. Sites that moved to the mixed group of other platforms fare slightly worse still, at 16.7% bad. A framework build likely needs its sitemap set up by hand, while WordPress generates one by default.
Old-domain and staging URLs barely show up: 5.2% of 367 switchers with a sitemap list any off-domain URL, and none listed a staging host.
What this means for your site
After a migration, crawl your sitemap, not just your site. Request every listed URL without following redirects and remove anything that does not return a 200.
- Make the sitemap use the same trailing slash format as your canonical URLs.
- Drop URLs whose canonical points elsewhere or that carry a noindex.
- On a framework build, generate the sitemap from the same route list the site uses, so retired pages leave both at once.
- Check the sitemaps report in Search Console after launch for errors and discovered URLs.
Sources
- PageSpeed Matters analysis of sitemap URLs on 361 sites that switched platform between September 2024 and September 2026, October 2026
- Google Search Central, build and submit a sitemap: https://developers.google.com/search/docs/crawling-indexing/sitemaps/build-sitemap
Embed this research
Paste this on your site to embed the chart. It links back to the source automatically.
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<script>window.addEventListener("message",function(e){if(e&&e.data&&e.data.psmEmbed==="post-migration-sitemaps"&&e.data.height){var f=document.getElementById("psm-post-migration-sitemaps");if(f){f.style.height=e.data.height+"px";}}});</script>
<p style="font:14px/1.5 system-ui,sans-serif">Source: <a href="https://www.pagespeedmatters.com/resources/data-studies/post-migration-sitemaps">Post-Migration Sitemaps: 1.7x More Bad URLs Than Average - PageSpeed Matters</a></p>
Frequently asked questions
How many bad URLs are in sitemaps after a migration?
On sites that changed platform, 7.3% of sampled sitemap URLs redirect or return a client error, against 4.3% on comparison sites. With canonical and noindex checks added on a subsample, 11.4% of listed URLs should not be in the sitemap.
What is the most common sitemap problem after a migration?
Redirects. 6.4% of the 10,062 checked sitemap URLs on switchers redirect, and 2.0% of all sampled URLs redirect only to add or drop a trailing slash.
Do migrated sitemaps list staging URLs?
Rarely. 5.2% of 367 switchers with a sitemap listed any off-domain URL, and none listed a staging host.
A sitemap that lists only live, canonical, indexable URLs is a quick fix after launch and gives search engines a clean map of the new site. Need help with this? See our SEO migration services.