PRIVATE BROWSER TOOL

Regex Tester

Test patterns, flags, groups, and match positions. Nothing is uploaded.

Input172 characters · 3 lines
Result0 matches
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Processed locally on this device.
Unicode-safe UTF-8 handling

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LOCAL-FIRST TEXT UTILITIES

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Your text never leaves this browser. No uploads, accounts, or server processing.

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About, editorial standards, and privacy

TESTING TOOLS · LOCAL PROCESSING

Test JavaScript regular expressions against real text

The Regex Tester runs a JavaScript regular expression against your sample text, highlights each match, and lists match positions and captured groups. Patterns execute locally, making it convenient for testing logs, content, and multilingual input.

COMMON USES

When this tool is useful

  • Develop a pattern for validation, extraction, or text cleanup.
  • Compare case-sensitive, global, multiline, and Unicode flag behavior.
  • Inspect capture groups and exact match positions before adding code.

THREE STEPS

How to use the Regex Tester

  1. Enter a JavaScript-compatible pattern and the flags you need.
  2. Paste representative text, including edge cases, into the input panel.
  3. Select Test, then review highlights, positions, and captured groups.

PRIVACY

Your input stays in this browser

The operation runs on your device and does not require the input to be uploaded. Copy and download actions happen only when you choose them. Avoid treating encoded output as encryption, and follow your own security requirements for confidential data.

WORKED EXAMPLE

Regex Tester: input and expected result

Input or settings

Pattern: hello
Flags: gi
Text: Hello, hello

Expected result

1. Hello · index 0
2. hello · index 7

Case-insensitive matching finds both spellings. Match positions are zero-based JavaScript string indices measured in UTF-16 code units.

METHOD & LIMITS

How the Regex Tester works

Processing method

The tester constructs a JavaScript RegExp, adds the global flag to collect matches, and displays matched text, positions, and capture groups.

What to review

JavaScript regex behavior can differ from PCRE, Python, or Java. Results stop at 500 matches, and expensive patterns can block the page; start with small samples.

References: JavaScript RegExp reference

PRACTICAL NOTES

What to know before using it

Which regex flavor is used?

Patterns follow the JavaScript RegExp behavior available in your current browser.

Can a regular expression freeze the page?

Pathological patterns can take a long time on some inputs, so test complex expressions with small representative samples first.