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Regex Tester

Test JavaScript regular expressions in your browser. Try patterns with flags, inspect matches and capture groups, and copy a match report - no upload required.

Regular expression

Enter a JavaScript pattern (without slashes) and choose flags.

Flags

No pattern yet

Enter a regular expression or load the example to start matching.

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Free utilities designed for privacy, speed, and everyday reliability.

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Version
1.0.0

Key Features

  • Live match inspection

    See every match with start/end indices, numbered capture groups, and named groups as you edit the pattern or test string.

  • Full flag support

    Toggle g, i, m, s, u, and y to mirror how your application will compile the expression.

  • Highlighted preview

    Matched spans are marked in a plain-text preview so you can verify boundaries before shipping the regex to production.

How to Use

  1. 1

    Enter a pattern

    Type the regular expression body without surrounding slashes. Enable the flags your runtime will use.

  2. 2

    Paste a test string

    Add the sample text, log line, or input you want to match against.

  3. 3

    Review matches

    Inspect match count, indices, groups, and the highlighted preview. Copy or download a report if you need to share it.

Use Cases

  • Building a form validation pattern

    Iterate on a regex for validating emails, phone numbers, or usernames against realistic sample inputs before shipping it.

  • Extracting fields from log lines

    Write and test a capture-group pattern that pulls timestamps, IDs, or error codes out of raw log output.

  • Reviewing a regex from a code review comment

    Paste a suggested pattern and sample text to confirm it behaves as claimed before merging a pull request.

  • Porting patterns between languages

    Check how a regex ported from another language behaves under JavaScript RegExp semantics, including flag and escaping differences.

Examples

Email-like tokens

Capture local and domain parts with groups.

Pattern: (\w+)@(\w+\.\w+) · Text: hello@toolmint.dev
1 match · group1=hello · group2=toolmint.dev

Global digit runs

Find every number with the global flag.

Pattern: \d+ · Flags: g · Text: order 12 and 7
2 matches: "12" and "7"

Case-insensitive word

Match a keyword regardless of case.

Pattern: error · Flags: i · Text: ERROR at line 9
1 match: "ERROR"

Benefits

  • Debug regex before dropping it into validation code
  • Confirm capture groups and named groups quickly
  • Share a match report with teammates
  • Keep sensitive log samples on your device
  • Mirror JavaScript RegExp behavior accurately

Best Practices

  • Prefer explicit character classes over overly greedy .* when extracting structured fields.
  • Enable the global flag when you need every match, not only the first.
  • Escape literal punctuation carefully - especially . ( ) [ ] { } + * ? ^ $ | \.
  • Test against realistic multiline samples when using ^, $, or the m / s flags.

Common Mistakes

  • Including /slashes/ around the pattern as if pasting a literal.
  • Forgetting the g flag and assuming every occurrence was checked.
  • Writing PCRE-only syntax such as lookbehind variants unsupported in older engines.
  • Using catastrophic backtracking patterns on large inputs and freezing the tab.

Privacy Notice

All pattern compilation and matching run in your browser. ToolMint does not upload, store, or transmit the pattern or test string you enter. After the page has loaded, you can continue testing offline.

About This Tool

What is this tool?

A Regex Tester is a developer tool that lets you write a regular expression, choose flags, and instantly see how it matches sample text. ToolMint’s Regex Tester uses the browser’s JavaScript RegExp engine so results align with typical frontend and Node.js code. It reports match positions, capture groups, named groups, and a highlighted preview so you can refine patterns with less trial and error.

Why use it?

Regular expressions are powerful and easy to get subtly wrong. A live tester reduces guesswork when validating emails, scraping log lines, extracting tokens, or writing replace rules. Because everything runs locally, you can paste proprietary log snippets and API payloads without uploading them. Clear match metadata shortens debugging cycles compared with console.log loops.

Limitations

This tool evaluates JavaScript regular expressions only. Patterns that rely on PCRE, Python, or .NET-specific features may not compile or may match differently. Pathological patterns can cause slow matching on large strings. The tester does not rewrite production code or guarantee security properties of user-supplied regex in server environments.

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