Regex Tester

Write and test regex patterns with sample input, flags, matches, groups, and replace.

Regex Tester

JavaScript (ECMAScript) regular expressions.

Max processed: 100,000 characters. Matches capped at 1,000.

Use $1, $2… for numbered groups, $& full match, $<name> for named groups.

Replace Output

—
Flags: /g/ • Matches: 1• Time: 0 ms

Highlighted Match

Matches & Groups

#1 [0–0):

Positional Groups

  • —

Named Groups

  • —

Matches (JSON)

[
  {
    "match": "",
    "index": 0,
    "groups": {},
    "captures": []
  }
]

What is a Regex Tester?

A regex tester is a tool for writing, testing, and debugging regular expressions: powerful pattern-matching syntax used in virtually every programming language. Regular expressions can validate email addresses, extract data from strings, find and replace text, parse log files, and much more. However, regex syntax is notoriously difficult to write correctly without instant feedback.

CodeHelper's Regex Tester highlights matches in real time, shows named groups, tests replacements, and includes a full cheat sheet and pattern library so you can write correct regex faster.

Key Features

  • Real-time Match Highlighting: Matches are highlighted in the test string as you type your pattern.
  • Capture Groups & Named Groups: View all captured groups and their values for complex extraction patterns.
  • Replace Preview: Test your .replace() pattern with a replacement string to verify the output.
  • Flags Support: Toggle global (g), case-insensitive (i), multiline (m), dotAll (s), and unicode (u) flags.
  • Pattern Library: A built-in library of common patterns: email, URL, IP address, date, phone number, and more.
  • Regex Cheat Sheet: Quick reference for metacharacters, quantifiers, anchors, and assertions.

How to test a regular expression

  1. Enter your regex pattern in the pattern field.
  2. Paste or type your test string in the input area.
  3. Matches are highlighted automatically in real time.
  4. Review groups and captured values in the results panel.
  5. Use the replace tab to test substitutions, then generate code for your language.

Whether you are validating form inputs in JavaScript, parsing log files in Python, or writing complex search patterns for a text editor, this free online regex tester is the fastest way to get your pattern right.

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