Speed & errors · nth Labs help

The free one, and the one to run most often. It measures rather than judges, so it returns the same answer twice, which is what makes it safe to put in CI.

What it measures

Core Web Vitals: LCP, CLS and the rest, taken in a real browser rather than estimated from a waterfall.
Accessibility, via axe-core, on every surface, at desktop and mobile widths.
Links that go nowhere, including the ones inside a component nobody has clicked since it shipped.
Console errors, attributed to the surface that produced them.
Dead controls: a button that is visible, enabled, and does nothing when pressed.

The dead controls are the point

The rest of that list is available elsewhere. This one is not, because it needs a browser to press the thing and watch what happens next. The canonical example, from our own fixture:

A run in progress: the console streaming what the browser is doing, page by page, as it drives the product. — Speed and errors is one browser pass over every surface in the profile, streamed as it happens.

A submit button is visible and enabled, but a required field is hidden and cannot pass validation. Clicking submit does nothing, and nothing on the page says why. The browser writes “An invalid form control is not focusable” to a console no visitor will ever open.

Nothing about that page looks broken. Every static check passes. The form has been dead since the day somebody hid that field.

Running it

node cli.cjs vitals
node cli.cjs vitals --devices desktop,mobile
node cli.cjs vitals --scenarios pricing,login

--scenarios narrows to surfaces the profile already declares. It cannot add one. See the profile.

In CI

It is deterministic, free and exits non-zero on new ship-blockers, which is the whole specification for a gate. Running it in CI.