A shared style keeps diffs about logic. PHP-FIG 23,464 publishes three layers:
PSR-1, Basic Coding Standard: UTF-8 without BOM, a file either declares symbols or has side effects, classes in StudlyCaps, methods in camelCase, constants in UPPER_CASE.
PSR-12, Extended Coding Style (2019, replacing the deprecated PSR-2): four-space indents, braces on their own line for classes and methods, visibility on every member.
PER Coding Style, a PHP Evolving Recommendation that "extends, expands and replaces PSR-12" and is revised as PHP changes: 3.0 was released on 14 July 2025, and 3.1, tagged on 13 August 2026, adds rules for property hooks, asymmetric visibility and the pipe operator.
Tools lag the spec: PHP-CS-Fixer 3.95.27 13,556 has @PER-CS3.0 but no 3.1 set, and PHP_CodeSniffer 4.0.4 1,557 ships PSR1, PSR2 and PSR12 but no PER standard. PSR-1's naming rules no formatter can apply for you.