It worked yesterday. Here's how to find out why.

Sites that nobody touched don't break for mysterious reasons; they break for about five predictable ones. Check in this order; it's sorted by how often each one turns out to be the answer.

1. A key expired or a card failed

Your app depends on other services (Supabase for data, Resend for email, OpenAI for AI features, Stripe for payments) and each has its own account status. Log into each service your app uses and look for red banners: expired trial, failed payment, revoked key. This is the single most common cause, and it produces exactly the "worked yesterday" pattern: the key worked until the moment it didn't.

2. A free-tier quota ran out

Same dashboards, different line: usage. Free tiers pause projects that exceed monthly limits (Supabase pauses inactive free databases too, which resurrects on its own the next day and is very confusing). If a quota is the cause, the site often half-works: pages load but data or features fail.

3. The domain or its paperwork lapsed

If the site doesn't load at all (rather than loading broken), check that your domain registration didn't expire and that the address still points where it did. Your registrar's dashboard shows both. Browser messages about "connection not private" point here too.

4. Something in the browser is failing

Open the site, press F12, click the Console tab, reload, and screenshot whatever's red. You don't need to understand it; that screenshot plus the prompt below is often the whole diagnosis.

5. The service itself is down

Rarely, it's not you: check the status page of your host and of Supabase/whatever you build on. If it's them, doing nothing is correct.

The fix prompt

Hearing about it before your users do

The expensive part of silent breakage isn't the fix, it's the not-knowing: sites stay broken for weeks because nobody was looking. A free uptime pinger on your main URL is the minimum. Plyo watches for you: live sites are checked every few minutes, real visitor errors are monitored, and when something breaks you get one email naming the likely cause in plain English, with a fix-prompt ready for your AI.