OnSubmit Free and fast tools
EN
English English EN Français Français FR Español Spanish ES Deutsch German DE Italiano Italian IT
Search
Development · free tool

Regex tester for JavaScript patterns, matches and replacements

Test JavaScript regular expressions, flags, matches and replacements. Your data stays in your browser whenever the task can be processed locally.

Use the tool Read the FAQ

Your tool

Regex Tester

Good to know

A regex tester runs a regular expression against sample text so you can inspect matches, flags and replacement behavior.

regex testerregular expressionjavascript regexpattern matchingjavascript regex tester

Understand

Understand Regex Tester

What is Regex Tester?

A regex tester runs a regular expression against sample text so you can inspect matches, flags and replacement behavior.

Main use case: Test a JavaScript regex pattern before using it in validation, extraction, cleanup or QA checks.

Common use cases

Form validation
Check patterns for emails, IDs, slugs or user input.
Text extraction
Extract repeated patterns from logs or copied text.
Replacement testing
Preview cleanup rules before using them in code.

How to use the tool

  1. Enter a regex pattern.
  2. Set JavaScript flags such as g or i.
  3. Paste sample text.
  4. Review matches and replacement output.

Best practices

  • Use realistic test values when validating forms, exports or API payloads.
  • Keep real customer, banking and production secrets out of public tools.
  • Check the output format before copying it into a production workflow.
  • Document whether a value is generated, validated, converted or only estimated.

Common mistakes

Confusing valid format with real-world validity
A generated or locally validated value can match a format without proving that it exists in an official system.
Using real production data
Public utilities are best for test data, demos, fixtures, QA and quick checks, not for confidential values.

Related terms and searches

regular expressionJavaScript regexflagsmatchesreplacementvalidationjavascript regex testertest regular expression onlineregex replacement tester

Continue with

Suggestions selected for the same workflow: validation, generation, conversion, test data or content preparation.

Development Development JSON Formatter JSON Formatter complements Regex Tester in the same development workflow. Continue Text Text Diff Checker Diff Checker is useful after Regex Tester when the workflow needs another format, validation step or test-data value. Continue Development Development URL Encoder / Decoder URL Encoder / Decoder complements Regex Tester in the same development workflow. Continue Utilities Utilities Word Counter Word Counter is useful after Regex Tester when the workflow needs another format, validation step or test-data value. Continue

FAQ

Frequently asked questions

Which regex flavor is used?

The tester uses JavaScript regular expressions, so behavior follows the browser RegExp engine.

Why can a regex be slow?

Some nested quantifiers can cause expensive backtracking. Simplify risky patterns before using them on large text.

Can I test replacements?

Yes. Enter replacement text to preview the transformed output.

Are my inputs sent to a server?

OnSubmit tools run in the browser whenever the task can be processed locally. Avoid pasting production secrets, real banking details or personal data into public tools.