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Merge Tailwind CSS class lists without style conflicts — a fast, independent PHP port of dcastil/tailwind-merge, ported directly from the JS source and not a fork of any existing PHP package.

If you are building a complex UI — you should componentize. And if you are using Tailwind and componentizing — you need Tailwind Merge.

Laravel glue ships in the box, so it's ready for Laravel too. The name tailwind-merge-php is deliberate: this is a framework-agnostic PHP package first, and a Laravel plugin second.

Tailwind CSS v4 only. (to v4.3) No legacy v3 config (no custom separators, TW3 theme keys, etc.). The v3-style leading ! important modifier is still parsed, matching upstream.
Fast. Class-map trie built once per instance, native string functions on the hot path, in-process LRU result cache. Roughly 50× faster than gehrisandro/tailwind-merge-php on the same real-world class lists even with the cache disabled, far more with a warm cache (note: that port targets Tailwind v3, this one v4). The benchmark itself was deliberately removed from the repo — it isn't part of the shipped package or the test contract.
Defensive. strict_types, final classes, PHPStan level max, invalid config keys and non-string class list entries rejected with InvalidArgumentException.
Test-based. The behavior contract is the upstream JS test suite: 371 tests / ~1,900 assertions, including 323 merge cases extracted from and verified against the real tailwind-merge npm package v3.6.0 (which targets Tailwind CSS v4).

Usage

use Stamat\TailwindMerge\TailwindMerge;

// Shared instance, default Tailwind v4 config
TailwindMerge::instance()->merge('px-2 py-1 bg-red-500 hover:bg-red-700', 'p-3 bg-[#B91C1C]');
// => 'hover:bg-red-700 p-3 bg-[#B91C1C]'

// Strings and nested arrays; null/false entries are skipped
TailwindMerge::instance()->merge('block', ['px-2', $isLarge ? 'text-lg' : null]);

Custom config

// Extend / override the default config (same semantics as extendTailwindMerge in JS)
$tw = TailwindMerge::create([
    'cacheSize' => 1000,
    'prefix' => 'tw',                       // for Tailwind's `tw:` prefix option
    'extend' => [
        'theme' => ['spacing' => ['my-space']],
        'classGroups' => ['shadow' => ['shadow-100', 'shadow-200']],
    ],
    'override' => [ /* replaces instead of appends */ ],
]);

// Or a fully custom config (see DefaultConfig::config() for the shape)
$tw = new TailwindMerge($fullConfig);

Laravel

Framework glue ships in the box and is auto-discovered — no manual provider registration. Install illuminate/support (already present in any Laravel app).

{{-- Blade directive --}}
<div class="@twMerge('px-2 p-4', $isActive ? 'bg-blue-500' : 'bg-gray-200')">…</div>

use Stamat\TailwindMerge\Laravel\Facades\TwMerge;
use Stamat\TailwindMerge\TailwindMerge;

TwMerge::merge('px-2 p-4', 'bg-red');   // facade
app(TailwindMerge::class)->merge(...);   // or resolve from the container

The container binds a single shared, configured instance. In a Laravel app, always resolve through the facade or container (as above) — not TailwindMerge::instance(). That static helper returns a separate instance built from the default config, ignoring anything you set in config/tailwind-merge.php (e.g. prefix, cacheSize), so the two can merge differently.

Publish the config to tune cacheSize, prefix, extend and override:

php artisan vendor:publish --tag=tailwind-merge

Development

composer install
composer test          # pest
composer test:types    # phpstan (level max)
composer lint          # pint

src/DefaultConfig.php is generated from the upstream JS package — do not edit by hand. The upstream version is pinned in bin/package-lock.json and stamped into the generated file header; bump bin/package.json to move it. CI regenerates and fails on drift.

cd bin && npm install && node generate-default-config.mjs

tests/Fixtures/merge-cases.json holds merge cases extracted from the upstream test suites and verified against the real JS implementation.

Disclaimer

This repo was built with AI — specifically Claude Fable 5 — as a model test, with explicit instructions to follow best practices such as strict test-driven and defensive coding.

I know there are several PHP ports of tailwind-merge, but after reviewing them, I've seen the areas they could be improved upon, so I decided to synthesize my own. I do need it for a project or two.

The main improvement is that the tests come straight from upstream and are treated as law: the behavior contract is the JS tailwind-merge test suite itself, not a hand-picked subset. If upstream and this port disagree, upstream is right and the port is the bug.

With 🫀 @stamat

stamat / tailwind-merge-php

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