sebastian/diff

diff is a standalone PHP library for computing and rendering textual differences, widely used to display “expected vs actual” output in testing tools. It supports line-based and character/word-granular comparisons so you can get both coarse and fine-grained views of changes. Output builders can produce formats like unified or context diffs, or more human-friendly renderings suitable for terminals and HTML reports. Internally, the library splits input into hunks and manages edge cases such as whitespace-only changes and end-of-line variations. Its abstractions make it straightforward to plug custom output styles or colorizers without reimplementing diff logic. Because it’s the diff engine under PHPUnit, it has been exercised across countless projects and edge cases.