Regex Tester

A regular expression (regex) tester is a tool that lets you write regex patterns and immediately see how they match against test strings. Regular expressions are a powerful pattern-matching language used across virtually every programming language — from JavaScript and Python to Java, Go, and Ruby — to search, validate, extract, and replace text.

Writing regex patterns can be notoriously tricky. A misplaced quantifier or forgotten escape character can mean the difference between matching email addresses and matching everything on the page. That's why real-time testing with visual feedback is essential: you can see exactly what your pattern captures, which groups it creates, and where it fails — all before deploying it in production code.

This regex tester provides instant match highlighting, capture group inspection (including named groups), and support for all standard JavaScript regex flags (global, case-insensitive, multiline, dotAll). Everything runs entirely in your browser — your test strings and patterns are never sent to a server.

1. Enter your regex pattern — Type your regular expression in the pattern field. The tool uses JavaScript's RegExp syntax, so patterns like \d+, [a-zA-Z]+, and (?<name>\w+) all work.
2. Toggle flags — Enable or disable flags: g (global — find all matches), i (case-insensitive), m (multiline — ^ and $ match line boundaries), and s (dotAll — . matches newlines).
3. Paste your test string — Enter the text you want to match against. Matches are highlighted in real time as you type.
4. Inspect match details — Each match shows its index position, full match text, numbered capture groups ($1, $2, ...), and named capture groups if present.

• Real-time match highlighting — Matches are visually highlighted in the test string as you type your pattern, giving instant feedback.
• Capture group inspection — View both numbered groups ($1, $2) and named groups ((?<name>...)) for each match, making it easy to debug extraction patterns.
• All JavaScript regex flags — Toggle global (g), case-insensitive (i), multiline (m), and dotAll (s) flags with a single click.
• Error reporting — Invalid regex patterns are caught and displayed immediately, so you know exactly what's wrong with your syntax.
• Match index positions — See the exact character index where each match starts, useful for understanding how your pattern traverses the input.
• 100% client-side — Your patterns and test data never leave your browser. No server, no tracking, no data storage.

• Email and URL validation — Test patterns like [\w.-]+@[\w.-]+\.\w+ to validate user input before deploying form validators.
• Log file parsing — Build regex patterns to extract timestamps, IP addresses, error codes, and other structured data from log lines.
• Data extraction with capture groups — Use groups to pull specific fields out of semi-structured text like CSV rows, HTML snippets, or API responses.
• Search and replace preparation — Test your find-and-replace patterns before running them across an entire codebase or document.
• Learning regex syntax — Experiment with quantifiers (*, +, ?, {n,m}), character classes (\d, \w, \s), and lookaheads/lookbehinds in a safe sandbox.