Thank you for your answer, but I think I haven't described it clearly enough: it wouldn't check for broken API links but it would be a REST API (a service) for checking broken links on any website - something like W3C checker.
That sounds more useful... but it's also something that most developers could probably build for themselves in a few minutes?
1. Grab page 2. Parse and find links 3. Make a request to each link 4. Return any links that are returning 4xx or 5xx.
Maybe there's a use for it where people want to test a particularly large set of pages/links making use of a data center's typically superior connection? shrug
Plus it would check not only links but also images, stylesheets, scripts, submitting forms - something like a 'website testing platform'.