Limits
Google documents that its crawlers follow up to 10 redirect hops by default. Its site-move guidance asks you to redirect old URLs directly to their final destination and, where that is not possible, to keep chains short: no more than three, and fewer than five.
Why they appear
Layered rules from the host, the CMS, a plugin and a migration map, or a second migration added on top of the first. A loop, where the chain returns to a URL it has visited, never reaches a page at all.
A worked example
Before: http://example.com/ redirects with a 301 to https://example.com/, which redirects to https://www.example.com/, which redirects to https://www.example.com/en/: three redirects and four requests for one visit. After: every old variant, and the HTTPS rule too, goes straight to https://www.example.com/en/, so any entry point costs one redirect. Each hop adds a round trip for visitors and a request for crawlers.
Redirect rules from different layers (host, CMS, plugin) can contradict each other. After changing one, test the four address variants again from outside, because a rule that works on the server may be overridden by a CDN in front of it.
What to check
Each important old URL and the four site variants, following redirects to the end, recording the number of hops and the final status. Fix by pointing each old rule at the final URL.
Sources
Read on . Standards and vendor pages change; confirm the current text before you rely on it.
- Google Search Central, How HTTP status codes, network and DNS errors affect Google Search (developers.google.com)
- Google Search Central, Site moves with URL changes (developers.google.com)