CodeHighlight

Installation

Install Alto Code Highlight in a PHP 8.4 or later application and verify the runtime before adding it to a page.

Requirements

Alto Code Highlight requires:

  • PHP 8.4 or later;
  • the mbstring extension;
  • the tokenizer extension;
  • Composer.

The package has no PHP package dependencies at runtime. It also needs no Node.js process or client-side syntax highlighter.

Install with Composer

Run this command in your project:

composer require alto/code-highlight

Framework applications normally load Composer's autoloader for you. In a standalone PHP script, load it explicitly:

<?php
require __DIR__.'/vendor/autoload.php';

Smoke test

Save this as highlight.php in the project root:

<?php

declare(strict_types=1);

require __DIR__.'/vendor/autoload.php';

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

$highlighter = new Highlighter(new AltoTheme());
$code = '<?php echo "Alto is ready";';

echo "<style>\n".$highlighter->getTheme()->getStylesheet()."\n</style>\n";
echo $highlighter->highlight($code, 'php');

Run it and write the resulting HTML to a file:

php highlight.php > highlight.html

Open highlight.html in a browser. It should contain a dark Alto code block with highlighted PHP.

Common installation failures

Composer rejects the PHP version

Check the CLI version used by Composer:

php --version
composer check-platform-reqs

The package requires PHP 8.4 or later.

A required extension is missing

Check both extensions in the same PHP runtime used by Composer:

php --ri mbstring
php --ri tokenizer

Install or enable the missing extension, then rerun Composer.

The autoloader cannot be found

Run composer install in the project and make the require path relative to the script that executes it. A framework bootstrap usually already includes vendor/autoload.php.

A language is reported as unsupported

Use an exact identifier from the language reference. The highlighter normalizes case and surrounding whitespace, but does not provide aliases such as js, ts, sh, yml, or cs.

Next step

Continue with Getting started for a complete page, line-number options, and error handling.