ERR_TOO_MANY_REDIRECTS on Netlify
Why it happens on Netlify
A catch-all rule in _redirects that matches its own destination path re-enters itself on every pass.
The fix on Netlify
Order rules from most to least specific and make sure no rule's destination can match its own source pattern. Use a 200 rewrite instead of a 301 where you want a proxy rather than a redirect.
Is ERR_TOO_MANY_REDIRECTS happening on your domain?
The uptime probe returns the full redirect chain, so you can see the exact two URLs bouncing off each other instead of inferring it from behaviour.
Free, no signup. Runs from outside your network, which is the only way to tell a server fault from a local one.
If that didn't fix it
Netlify has its own failure mode, but ERR_TOO_MANY_REDIRECTS has a wider set of causes that apply everywhere. The most common one overall is: the cdn forwards to the origin over http while the origin redirects all http to https — an infinite loop.
All causes and fixes for ERR_TOO_MANY_REDIRECTS