Browser Compatibility Checker: Baseline Web Feature Support

Shipping a modern web app means constantly asking: does this API work in the browsers our users actually run? The Browser Compatibility Checker answers that with a curated, offline reference aligned to the Web Platform Baseline.

What Baseline means

Status	Meaning
Baseline widely	Supported across major browsers long enough for default use
Baseline newly	Recently crossed the Baseline bar — safe for most new projects
Limited availability	Uneven support — plan fallbacks or progressive enhancement

Baseline is not a guarantee for every user (enterprise policies, old devices, and embedded WebViews still matter), but it is the industry shorthand for “safe to adopt without a polyfill stack.”

Example: `:has()` selector

Parent-aware styling used to require JavaScript. CSS :has() fixes that — but only where browsers ship it.

Search has in the tool and you will see:

Baseline status: newly
Chrome 105+, Firefox 121+, Safari 15.4+

If your analytics show Safari 15.3 traffic, you still need a fallback even though the feature is Baseline newly.

Why embedded data?

Many compatibility sites fetch live JSON or scrape MDN. This tool embeds its catalog so:

Privacy — no third-party requests while you explore features
Speed — instant search on slow conference Wi‑Fi
Offline — works during flights or air-gapped reviews

The trade-off: the dataset updates on release cadence, not hourly. For launch-critical decisions, cross-check your analytics browser mix.

Related workflows

Parse a visitor string with the User Agent Parser to see engine and version
Test layouts across breakpoints with the Flexbox Playground
Pair Baseline checks with feature flags or @supports rules in CSS

Limitations

Covers Chrome, Firefox, and Safari minimums — not Edge version numbers (Chromium-aligned) or Opera
Does not replace automated @supports / CSS.supports() tests in CI
Limited-status APIs (Web Push on Firefox, Credential Management on Safari) need explicit product decisions

Use the checker during design and code review; validate in real browsers before you merge.