If you find Xdebug useful, please consider supporting the project.

Xdebug 3 — Documentation

Installation

Installation
FAQ
Description of errors

Features

Step Debugging
Profiling
Development Helpers
Function Trace
Code Coverage Analysis
Flame Graphs

Tools

Command Line Debug Client
The command line debug client allows you to debug PHP scripts without having to set up an IDE.
DBGp Proxy Tool
This tool allows you to proxy and route debugging request to IDEs depending on which IDE key is in use.
Xdebug Control
A command line tool to instruct Xdebug's step debugger to connect to the IDE or pause execution.

Compatibility

Supported Versions and Compatibility
Upgrading from Xdebug 2 to 3

Community

Contributing
A guide on how to contribute bug fixes and new features.
DBGP - A common debugger protocol specification
Describes the protocol that Xdebug uses for communicating with IDEs.

Reference

All Settings
All configuration settings documented on one page in alphabetical order.
All Functions
All Xdebug's functions documented on one page in alphabetical order.
Related Content
A list of all related content, such as videos that explain Xdebug and its features.