Documentation
Every external reference in your docs is a promise you can't keep alone
A documentation site is a collection of promises about URLs you do not control. API reference, authentication guides, status pages, SDK repos, RFC links, “see also” rows. When one of those moves, the docs become a confident lie.
Docs are a promise about someone else’s URL
You wrote “see the vendor’s guide for the webhook payload” and linked it. Six months later the vendor moved the guide, kept the URL, and the payload in your example is now wrong. The link still returns 200. That is the failure mode documentation teams actually have.
What actually breaks
The 404 is rare. Vendors redirect. They rewrite in place. They keep the URL and change the contract. A checker that only looks at status codes will give you a green report the week after the v2 endpoint stopped meaning what your example said. Content drift is the feature that notices; the fingerprint ignores nav on vendor doc sites that restyle constantly.
A small list is enough
Documentation teams with a few dozen external references are exactly the customer the €6 Daily Sweep add-on exists for. You do not need 1,500 URLs. You need to know when a page you cited stopped saying it.
How to set it up
A project called “External refs”, a paste of the list, content drift on, a digest to the person who can edit the docs. Accept-as-baseline when a vendor genuinely moved the canonical guide. Retry-before-flag so you are not paged by a status page blip.
We do not yet have a REST API or webhooks — email is the delivery channel. If your workflow is “open a GitHub issue when a ref drifts”, you will copy from the digest until we ship those. We will not pretend they exist today. Start on Daily Sweep plus drift, or Deep Sweep if the list will grow.