Regex Tester

Overview

• Runs a regular expression pattern against actual test text and shows the matched positions and capture groups.

• Since you can tweak the pattern little by little and immediately see whether it matches as intended, this is well suited to writing and debugging regular expressions.

• Uses JavaScript's regular expression engine (RegExp) directly, so it behaves the same as the regex you'd use in actual code.

Usage

1. 1

   Enter a regular expression pattern and flags (such as g, i, m).

2. 2

   Enter the text you want to test against in the text area.

3. 3

   Click the "Test" button to see a list of matched positions and capture groups.

Example

Pattern: \d{3}-\d{4} / Flags: g / Text: 090-1234 / 080-5678

1: 090-1234 (index: 0)
2: 080-5678 (index: 11)

Use Cases

• Building a validation regex (such as an email or phone number format check) while trying it against real data

• Verifying that a regex already used in code behaves as intended, using test cases that include edge cases

• Iterating on a regex to extract lines matching a specific pattern from logs, trying it against real log text

• Building a regex to detect or replace mixed line break codes (\r\n, \n, \r) in text, testing it against real text

FAQ

Notes

• Up to 1000 matches are displayed. If there are more, only the first 1000 are shown.

• You can specify flags supported by JavaScript regular expressions, such as g, i, m, s, u, and y. Without the g flag, only the first match is targeted.

• If the entered regular expression is syntactically invalid, an error message with specific details is displayed.

• Nested repetition such as "(a+)+" can make processing time explode on longer text (ReDoS). To keep the page responsive, processing that takes more than 2 seconds is stopped and an error is shown.