Using breakpoints to debug PHP code

Breakpoints pause an executing program at a line or condition to inspect why an input leads to a particular branch.

What It Does

Break on the age comparison to inspect the decision. Use a conditional stop for a failing boundary.

Requirements and Compatibility

Use a supported PHP runtime and install any third-party tool or extension explicitly shown in the examples. Commands should be run from the project root unless stated otherwise.

Syntax, Inputs and Results

The examples separate configuration, the smallest working operation and a realistic follow-up task. Adapt file paths and dependency versions to your own project.

Example 1: Basic Use

Break on the age comparison to inspect the decision.

<?php
function eligible(int $age): bool {
    if ($age < 18) return false;
    return true;
}
echo eligible(20) ? 'yes' : 'no';

Example 2: Another Case

Use a conditional stop for a failing boundary.

Condition: $age === 17
Inspect: $age and call stack
Continue: observe the false branch

Practical Example

Check debugger readiness in the same PHP environment.

php -i | grep -E 'xdebug.mode|xdebug.start_with_request'
XDEBUG_TRIGGER=1 php bin/check-eligibility.php

For production, apply the compatibility and edge-case limits described below.

Important Behavior and Edge Cases

A breakpoint that never triggers may indicate an unexecuted branch, incorrect path mapping or disabled debugger mode.

Comparison with Related Functions and Tools

Subject	Key difference
Step debugging vs profiling	Step debugging pauses individual statements; profiling records aggregate runtime cost.

Common Beginner Mistakes

Mistake	Correct approach
Enabling the debugger for every production request	Use controlled triggers and disable development modes in production.
Skipping the prerequisite of this specific workflow	Install or configure the named tool and confirm the example can actually run.
Ignoring edge conditions	A breakpoint that never triggers may indicate an unexecuted branch, incorrect path mapping or disabled debugger mode.

Key Takeaways

Breakpoints pause an executing program at a line or condition to inspect why an input leads to a particular branch.
A breakpoint that never triggers may indicate an unexecuted branch, incorrect path mapping or disabled debugger mode.
Keep application configuration, source code and validation tests under version control.

Use these examples as a starting point, then validate the result with the actual PHP build, dependencies and inputs used by your application.