First, Drag and drop your PHP file or copy / paste your PHP text directly into the editor above.
Finally, you must click on "Check PHP syntax" button to display if there is an syntax error in your code.
To run and execute your PHP code in your browser,
it is analogous to the check syntax code, except that you must click on "RUN PHP code (ALPHA)" button.
PHP code checker
PHP is a server-side scripting language, but can also be used as a general-purpose programming language.
PHP error checker tool allows to find syntax errors (lint).
If a syntax error is detected, then the line in error is highlighted, and it jumps to it to save time (no need to search the line).
It can be useful to make online test to save time (deployment ...).
PHP sandbox (Alpha version)
You can test your PHP code online directly in your browser (php fiddle),
It is a alpha version, it only supports a small subset of PHP.
You can not rely on this tool to validate the functionality of your php script.
I do not have the necessary infrastructure to run a PHP source code using a real binary safely.