PHP Debugger: A Lightweight Xdebug Alternative Built for Speed

PHP Debugger is a new PHP extension forked from Xdebug that removes everything except step debugging — no profiler, no code coverage, no tracing. The goal is a drop-in replacement that carries far less overhead when the debugger is loaded but not actively in use.

#Near-Zero Idle Overhead

Benchmarks using Valgrind instruction counting (run in GitHub Actions across PHP 8.2–8.5) show the overhead when the extension is loaded with no IDE connected:

#Drop-In Xdebug Replacement

PHP Debugger accepts both php_debugger.* and xdebug.* INI prefixes, so existing configurations work without changes:

; Your existing Xdebug config works as-is:
xdebug.mode = debug
xdebug.client_host = 127.0.0.1
xdebug.client_port = 9003
xdebug.start_with_request = trigger
 
; Or use the new prefix:
php_debugger.mode = debug
php_debugger.client_host = 127.0.0.1
php_debugger.client_port = 9003
php_debugger.start_with_request = trigger

The extension also reports true for extension_loaded("xdebug"), which means packages that check for Xdebug at runtime will continue to work. PhpStorm and VS Code both work without any configuration changes.

#Debug-Only Focus

By removing profiling, tracing, and code coverage, the extension stays focused on one use case: setting breakpoints and stepping through code.

If you need code coverage, the project recommends pcov as a separate extension.

#New PHP Debugger-Specific API

Alongside full Xdebug compatibility, the extension exposes its own function names and triggers as optional alternatives:

// Xdebug-compatible (still works):
xdebug_break();
 
// PHP Debugger equivalents:
php_debugger_break();
php_debugger_info();
php_debugger_connect_to_client();
php_debugger_is_debugger_active();
php_debugger_notify();

Session triggers follow the same pattern. XDEBUG_SESSION, XDEBUG_SESSION_START, and XDEBUG_TRIGGER all work, and the new PHP_DEBUGGER_SESSION, PHP_DEBUGGER_SESSION_START, and PHP_DEBUGGER_TRIGGER equivalents are available as well.

#Installation

Binaries are available on the releases page. After downloading the right binary for your PHP version, add the extension to your php.ini:

zend_extension=php_debugger.so

The project is also an interesting case study in AI-assisted development. According to the README, the entire extension — fork, strip, optimize, rename — was built in days using PhpStorm, Claude Code, and OpenClaw.

You can get started with this extension on GitHub.