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Developer & Data

Regular Expression Tester

Run JavaScript regex matching, group extraction and replacement in an isolated worker with a timeout.

◈ Local Processing · Inputs Are Not Uploaded

Inputs & Settings

This workspace processes data in the current browser; input is not saved upon refresh.

Results workbench

Fill in the details, then click Generate Results.

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Results will be displayed here

Review details, copy or download, and then continue your work.

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How to use Regular Expression Tester

  1. Enter original text and a JavaScript regular expression to perform match, extract, or replace operations.
  2. Enter 0 (full match) or group index when extracting; enter replacement template when replacing.
  3. Inspect match locations and updated outputs before copying or downloading. Timed-out requests will halt automatically without forcing continuation.

Try a concrete example

Use FAN-(\d+) to find FAN-001 and FAN-002. Group 1 extracts 001 and 002; replacement EC-$1 yields EC-001 and EC-002.

How to interpret results

Use JavaScript RegExp syntax and separate flags. Execution stops after one second. Input is limited to 200,000 characters and patterns to 2,000. Preview limits do not silently truncate replacements; total output is bounded. Matches do not establish business validity.

Frequently asked questions

Do I need to include slashes on both ends?

Enter only the expression body (e.g., \d+); flags are entered separately.

Why did only the first match register?

Check whether the g flag is enabled.

Can regex fully parse HTML from any arbitrary webpage?

Not recommended; complex HTML should be parsed using a proper parser.

regular expression tester practical guide and common questions

What does a regular expression tester do?

Regular expressions describe character patterns for matching, grouped extraction and replacement of identifiable text fragments.

Who is this for, and when is it useful?

Developers and content teams refining extraction or text-cleaning rules.

How do I use this regular expression tester?

Enter representative text, a pattern and flags, inspect matches and offsets, and include empty, boundary and nonmatching examples.

How should I interpret the results?

Test representative boundaries and replacement groups, and inspect flags such as g and i. JavaScript syntax differs from some other engines; simplify patterns stopped by the time limit.

Where is the work performed, and which services receive data?

JavaScript regular expressions run in an isolated browser Worker with a time limit. Input scripts are not executed and embedded URLs are not requested.