# Baseline support overview

> What Baseline means, the widely-available / newly-available / limited-availability tiers, the seven tracked browsers, the 30-month window, and Baseline 2026 as the currently developing yearly cohort.

**In one line:** Baseline is a cross-browser-support signal for web platform
features — APIs, CSS properties, and JavaScript syntax — expressed as one of
three tiers (widely available, newly available, limited availability) based on
consistent support across seven browsers; "Baseline 2026" is the yearly cohort
of features currently crossing into newly-available status this year.

## The seven browsers Baseline tracks

Per MDN, Baseline considers support across a fixed set of browser/platform
combinations: Safari (iOS), Safari (macOS), Chrome (Android), Chrome
(desktop), Edge (desktop), Firefox (Android), and Firefox (desktop).

## The three tiers

| Tier | Definition |
|---|---|
| Widely available | "A consistent history of support in each of the Baseline browsers for at least 2.5 years" |
| Newly available | Works "in at least the latest stable version of each of the Baseline browsers, but may not work with older browsers and devices" |
| Limited availability | "Not yet available in all browsers" — the default tier for anything missing from at least one of the seven |

The 2.5-year figure is a 30-month window: a feature must have been
consistently supported across all seven Baseline browsers for at least that
long before it graduates from newly available to widely available.

## Yearly cohorts, and what "Baseline 2026" means

Features are also grouped by the calendar year in which they crossed into
newly available. Per web.dev, "all items that become part of Baseline Newly
available in 2024 can be referred to as Baseline 2024" — the same pattern
applies to other years. 2026 is described as "the latest and currently
developing feature set," meaning Baseline 2026 is not yet a closed, finalized
list — it accumulates newly-available features as the year progresses.

## What Baseline does not cover

MDN is explicit that "Baseline is a summary of browser support. It is not a
substitute for accessibility, usability, performance, security, or other
testing." It also may not account for older devices and browser releases,
browsers outside the tracked set such as operating-system web views, or
assistive technology such as screen readers.

## Where to check Baseline status

Per web.dev, Baseline is now defined by the WebDX Community Group. MDN's own
Baseline reference lists the `web-platform-dx/web-features` repository, the
WebDX Community Group, and `mdn/browser-compat-data` under "See also" as
related resources. Baseline status can be checked on MDN and on Can I Use, and
it is surfaced by tooling including Lighthouse audits, Chrome DevTools,
ESLint, Browserslist queries, VS Code, and a Netlify extension.

## Practical checklist

- [ ] Treat "widely available" as safe to use without a fallback for
      mainstream production traffic; treat "newly available" as safe only if
      your audience runs current browsers.
- [ ] Check Baseline status on MDN or Can I Use before shipping a new API,
      CSS property, or JS syntax feature.
- [ ] Remember Baseline covers only the seven tracked browser/platform
      combinations — verify separately for OS web views and assistive
      technology if your audience relies on them.
- [ ] Don't treat Baseline as a substitute for accessibility, performance, or
      security testing — it measures browser support only.
- [ ] For any feature, the widely-available date is roughly 30 months after
      *that feature's own* newly-interoperable date — not 30 months from the
      "Baseline 2026" label or from today; features that entered the cohort
      earlier in the year already have less than 30 months left.