Regex Tester

Test JavaScript regular expressions, inspect matches, and preview replacements.

Interactive workspaceChanges stay on this device
//
Replacement (optional)
2 matches
AdaIndex 0
LinusIndex 20
Private by defaultYour inputs and files are processed on this device.
Free and instantNo account, queue, or software installation required.
Ready to useCopy or download results as soon as they are generated.

How to use Regex Tester

Get a reliable result in three straightforward steps.

  1. 01

    Write a pattern

    Enter the expression without surrounding slash characters and add the flags you need.

  2. 02

    Add a test string

    Use representative text including expected matches and edge cases.

  3. 03

    Inspect or replace

    Review match positions and groups, then preview an optional replacement.

Built for everyday work

Useful without the busywork

Focused controls, immediate feedback, and no account between you and the result.

Live validation

Syntax errors are displayed as the expression changes.

Match details

Inspect values, positions, and captured groups.

Replacement preview

Test $1 groups and replacement behavior before using code.

Practical guide

What is Regex Tester?

A regular expression describes a text-search pattern using literals, character classes, groups, quantifiers, anchors, and flags. A tester makes those patterns easier to refine against realistic input.

This tool uses the JavaScript regular-expression engine, so supported syntax and flags follow the browser's ECMAScript implementation. Patterns from other languages may behave differently.

Practical applications

When to use this tool

Common ways Regex Tester fits into real projects and daily tasks.

1

Form validation

Prototype patterns for IDs, labels, and controlled input formats.

2

Log analysis

Extract values from consistent diagnostic lines.

3

Text cleanup

Preview pattern-based replacements before applying them elsewhere.

4

Development

Debug expressions used by JavaScript applications.

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Helpful answers

Frequently asked questions

Quick answers about regex tester and how this page works.

Should I include surrounding slashes?

No. Enter only the pattern; flags have their own field.

Why is the global flag added during matching?

The inspector scans globally so it can display every match, while replacement uses your selected flags.

What are capture groups?

Parenthesized subpatterns capture portions of a match for inspection or replacement references such as $1.

Will the same regex work in every language?

Not always. Syntax, Unicode handling, and available features differ across engines.