Regex Тестер

What is Regex Тестер?

A regex (regular expression) tester evaluates a pattern against a test string and shows all matches in real time. Regular expressions describe text patterns using a concise formal language — literals, character classes, quantifiers, anchors, and groups. The tester reports the full match, captured groups, match indices, and total match count, making it indispensable for developing and debugging patterns before deploying them in code.

How It Works

The tool compiles the user's pattern with the supplied flags (g, i, m, s, u, y) via the native RegExp constructor. For global patterns it iterates exec() to collect every match; without the g flag it shows only the first. Each match's value, index, and captured groups are displayed alongside the highlighted input. Invalid patterns surface a SyntaxError with the problematic token. The dotAll (s) and unicode (u) flags enable modern behavior.

Common Use Cases

• Building input validators — develop and test email, phone, or password patterns before coding
• Extracting data from logs — craft a capture pattern and verify it against sample log lines
• Refactoring find-replace — test a search pattern and its replacement against real text
• Learning regex syntax — experiment with quantifiers, anchors, and groups interactively

Technical Details

Engine: native JavaScript RegExp (ECMAScript 2024). Flags: g (global), i (ignore case), m (multiline), s (dotAll), u (unicode), y (sticky). Backreferences and named captures (?(<name>)) are supported. Catastrophic backtracking can hang the engine — the tool runs on the main thread, so pathological patterns may freeze the tab. No external regex engine is used.