README

Syntax highlighting for PHP projects

Server-side highlighting for the full PHP stack: 27 languages covering PHP, HTML, Twig, JavaScript, CSS, YAML, and more. Zero dependencies, semantic PHP syntax understanding definitions vs. calls, embedded language support, and 490+ compatible themes. Works in Twig templates, Laravel Blade, Symfony controllers—anywhere PHP runs.

Features

Built for PHP ecosystems: Highlight the full stack—PHP, HTML, Twig, JavaScript, CSS, SQL, YAML, and 20+ more languages in a single library.
Zero dependencies: No Node.js, Python, or external processes. Just Composer. Works in any PHP 8.4+ environment.
Full PHP syntax: Semantic parser that understands context—distinguishes class User (definition) from new User() (usage), function greet() ( definition) from greet() (call).
Embedded languages: Automatically switches parsers for <style> and <script> tags in HTML, fenced code blocks in Markdown, and {% block css %} in Twig.
Dark mode support: Multiple dark themes included out of the box ( CupertinoDark, Dracula, Noctis) plus compatibility with 490+ Highlight.js and Prism themes.

Install

composer require alto/code-highlight

Usage

use Alto\Code\Highlight\Highlighter;
use Alto\Code\Highlight\Theme\GitHubTheme;

// 1. Initialize with a theme
$highlighter = new Highlighter(new GitHubTheme());

// 2. Output the theme's CSS (typically in your <head>)
echo "<style>" . $highlighter->getTheme()->getStylesheet() . "</style>";

// 3. Highlight your code
echo $highlighter->highlight($code, 'php');

Languages

PHP

Alto uses a semantic parser for PHP that goes beyond pattern matching to understand code context. It correctly distinguishes between:

Definitions vs. usage: class User vs. new User(), function greet() vs. greet()
Context-aware scoping: Variables, function calls, class instantiation, method calls

Embeddings

Four languages support automatic embedded language detection:

HTML — CSS in <style> tags, JavaScript in <script> tags
SVG — CSS in <style> tags, JavaScript in <script> tags
Markdown — Any language in fenced code blocks (```language)
Twig — Languages via block names ({% block css %}, {% block javascript %})

Full list

Category	Languages
Programming	Bash, C#, Go, Java, JavaScript, PHP, Python, Ruby, Rust, Swift, TypeScript
Markup	HTML, SVG, XML
Data	Diff, DotEnv, HTTP, JSON, YAML
Prose	Markdown
Query	SQL
Stylesheet	CSS, SCSS
Template	Twig
Config	Dockerfile, INI, Makefile

Themes

Built-in themes

Alto includes 7 built-in themes ready to use:

Light themes: Alto, GitHub, Polar, Solar
Dark themes: CupertinoDark, Dracula, Noctis

use Alto\Code\Highlight\Theme\DraculaTheme;

$highlighter = new Highlighter(new DraculaTheme());

Dark mode

Three dark themes are included out of the box:

CupertinoDark — macOS-inspired dark theme
Dracula — Popular dark theme with vibrant colors
Noctis — Low-contrast dark theme for extended coding sessions

Compatibility

Use existing CSS from the Highlight.js (240+ themes), Prism (250+ themes), or TextMate (.tmTheme) ecosystems:

use Alto\Code\Highlight\Adapter\HighlightJsThemeAdapter;

$theme = HighlightJsThemeAdapter::fromFile('/path/to/github-dark.css');
$highlighter = new Highlighter($theme);

use Alto\Code\Highlight\Adapter\TextMateThemeAdapter;

$theme = TextMateThemeAdapter::fromFile('/path/to/monokai.tmTheme', isDark: true);
$highlighter = new Highlighter($theme);

Integrations

Twig Extension

Twig Extension — Highlight code directly in Twig templates using blocks or filters.

Contributing

Contributions are welcome! Please feel free to submit issues or pull requests.

License

Released by the Alto project under the MIT License. See the LICENSE file for details.

alto / code-highlight

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