For a React app, or other SPA, what's a good way of checking the web app (FE + API) is behaving correctly? Downloading a js bundle from a web server is not actually _running_ it.

I know that "behaving correctly" is a bit vague, so to be more precise: I might want to collect metrics for page load times, error rates, etc, in the SPA and then ship these to a back-end logging/metrics db as SLIs and then build alerts and dashboards off that to track error budgets and SLO conformance.

I could use Cypress.io, or Playwright.dev, but these are really headless browser testing tools, and are maybe a bit heavyweight for this use case. I'm wondering if there a better option here? Is it Sentry.io (although this also feels quite heavy)?

FOSS tools would be preferable -- do you know any?