Regex Tester

Test regular expressions against sample text and see matches live.

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How to use Regex Tester

Three quick steps — no sign-up needed

  1. Step 1

    Enter a pattern and flags

    Type the regular expression and any flags supported on the form.

  2. Step 2

    Paste a test string

    Provide sample text that should or should not match.

  3. Step 3

    Review matches

    Inspect highlighted or listed matches and adjust the pattern until it behaves correctly.

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About Regex Tester

Regex Tester lets you try regular expressions against sample text and inspect matches before shipping patterns to production. Developers searching "regex tester", "regex online", or "test regular expression" need rapid feedback on capture groups and flags.

Enter the pattern, set flags, paste a test string, and review matches. Flavour differences exist (JavaScript vs PCRE vs Python) - write patterns for the engine you deploy, not only the browser tester.

Catastrophic backtracking can freeze naive engines on crafty input. Prefer simpler patterns for user-provided data and set timeouts in server-side validation.

A development aid - not a guarantee of security for input validation alone.

Benefits of Regex Tester

Live match feedback See what the pattern captures immediately.
Flags support Experiment with case-insensitivity and multiline options where available.
Safer iteration Fix regex before it hits production logs.
Learning tool Great for understanding groups and quantifiers.

Frequently asked questions

Which regex flavour is this?

Browser-oriented JavaScript-style matching is common - confirm against your runtime.

What are flags?

Modifiers such as case-insensitive or global matching depending on the engine.

Why is my pattern slow?

Ambiguous quantifiers can backtrack heavily - simplify the expression.

Can it replace text?

Focus is testing matches; replacement may be a separate step in your editor.

Is regex enough for HTML parsing?

Usually no - use an HTML parser for markup.