Browsers & devices

Supported browsers

Bootstrap supports the latest, stable releases of all major browsers and platforms, plus a run of older versions of each engine. The exact policy lives in our .browserslistrc file:

last 2 major versions
not dead
unreleased versions

Chrome >= 130
Edge >= 130
Firefox >= 132
iOS >= 18.0
Safari >= 18.0

not and_uc > 0
not and_qq > 0
not kaios > 0
not op_mini all

Browserslist joins these lines with OR, not AND. The >= lines do not narrow last 2 major versions. They add every version above each floor, which is what sets our real minimums:

Alternative browsers built on these engines (Chromium-based browsers like Brave, Opera, or Vivaldi, and browsers using WebKit on iOS) are not explicitly tested, but should be fully supported at equivalent engine versions.

How to read the query list

Two of those lines do more than they look like they do:

• last 2 major versions carries our mobile coverage. caniuse tracks Chrome for Android as a single unversioned entry rather than one entry per release, so this line, not the >= floors, is what picks it up.
• unreleased versions is worth about eight points of coverage, and it costs nothing. caniuse gives the newest Safari a null release date, yet that version already holds most of Safari’s usage share. Both range queries and last N versions skip unreleased versions, so without this line we would exclude the single most-used Safari. It cannot pull in anything old, because an unreleased version is newer than every floor.

To measure coverage yourself, run npx browserslist --coverage in a clone of the repository. Do not read the figure off browserslist.dev: that site pins an older copy of caniuse-db and reports a materially different number.

Why these versions?

Bootstrap’s CSS is written against the modern platform baseline: light-dark() for color modes, oklch() and color-mix() for the color system, native CSS nesting, container queries, and :has().

Our floors also have to last. They apply to the whole v6.x line, and we cannot raise them in a minor release, so they cap what every future 6.x feature may use. We therefore set each floor on the newest feature v6 already depends on, not the oldest version we could tolerate:

light-dark() sets the hard lower bound: Chrome 123, Firefox 120, and Safari 17.5. Below it, our build pipeline lowers light-dark() to a custom-property polyfill, and that polyfill breaks data-bs-theme dark mode. We will not go below that bound in any release.

Together these targets cover about 85% of global browser usage.

Unlike previous major versions, Bootstrap 6 does not ship fallbacks, prefixes, or polyfills for browsers below this floor. Pages will not render correctly in unsupported browsers—most visibly, colors depending on light-dark() will not resolve.

Modern platform features

The table below lists the platform features v6 relies on and how each behaves at—and below—the support floor.

Also safe to use

The floors clear more of the platform than the components currently use. All of the following need no fallback, no vendor prefix, and no polyfill in any 6.x release, so reach for them first when you build on top of Bootstrap or contribute to it:

• Native CSS nesting, so compiled output can stay nested
• @layer, which our layer order depends on
• :focus-visible for keyboard-only focus styling
• Container query units and subgrid
• content-visibility, transition-behavior: allow-discrete, and @starting-style, which together animate <details> and <dialog> open and closed
• Unprefixed backdrop-filter
• text-wrap: balance
• Range syntax in media queries, such as @media (width >= 1024px)

Not available yet

These features sit above our floors, so v6 cannot use them without a fallback. Firefox is the blocker in nearly every case, which means Chrome support alone is never enough to tell you whether we can ship something.

Relative color syntax is the closest miss, one version above our Chrome floor. Anchor positioning is the one most worth waiting for: it would let Menu, Tooltip, Popover, and Combobox drop their Floating UI dependency. Re-check these with npx browserslist before you assume one has landed.

JavaScript

Bootstrap’s JavaScript ships as native ES modules only. Load it with <script type="module">—a classic <script src> without type="module" will not execute it, and there is no global window.bootstrap object. See the JavaScript getting-started guide for loading patterns, including import maps for the bundle’s dependencies.

All browsers meeting the CSS support floor above fully support ES modules, import/export syntax, and the DOM APIs Bootstrap’s plugins use—no transpilation or polyfills are required or provided.

Mobile devices

Generally speaking, Bootstrap supports the latest versions of each major platform’s default browsers. Note that proxy browsers (such as Opera Mini, Opera Mobile’s Turbo mode, UC Browser Mini, Amazon Silk) are not supported. We also exclude UC Browser, QQ Browser, and KaiOS. Together they hold under 1% of users, and including them only adds vendor prefixes to our CSS: -webkit-mask-* for UC and QQ, and -moz-column-gap for KaiOS. KaiOS additionally broke our floating labels.

As with v5, make sure you include the responsive viewport meta tag in your <head> for proper rendering on mobile devices:

<meta name="viewport" content="width=device-width, initial-scale=1">