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Regex Tester

Regex

Test regular expressions with live matching

Building a regular expression by trial and error against your actual code is slow and error-prone; this gives you live match highlighting as you type a pattern next to a test string, plus per-flag toggles (global, case-insensitive, multiline) so you can see exactly how each one changes what matches. It runs on JavaScript's native RegExp engine, which is close to but not identical to PCRE or the regex flavors in Python and Go, so a pattern that behaves correctly here should still be checked against your actual runtime before shipping, especially around lookbehind support and named groups. If you don't know where to start with syntax, the companion Regex Cheatsheet has a reference table, and NL → Regex can turn a plain-English description into a first-draft pattern.

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How to use Regex Tester

  • 1.Type a pattern and test string side by side to see live match highlighting as you build your regular expression.
  • 2.Toggle flags (global, case-insensitive, multiline) to see exactly how they change which parts of your text match.
  • 3.Use capture groups in your pattern to see each group's matched value broken out separately, useful for extracting structured data from text.

Frequently asked questions

What regex flavor does this use?
This tool uses JavaScript's native RegExp engine (ECMAScript regex syntax), which is very close to PCRE but has some differences — notably around lookbehind support in older engines and named group syntax.
Why does my pattern match in this tool but not in my backend language?
Different languages (Python, PHP, Go) use different regex engines with subtly different syntax for things like lookaheads, Unicode properties, and possessive quantifiers — always test against your actual runtime for production use.
Can I test multiline input?
Yes, enable the multiline (`m`) flag so `^` and `$` match the start/end of each line instead of only the whole string.
I don't know regex syntax — is there help?
Yes — try the NL → Regex (AI) tool to describe what you want to match in plain English and get a working pattern with an explanation, or check the Regex Cheatsheet for a quick syntax reference.

Use via API, SDK, or MCP

cURL# Free: 1,000 req/day · Pro: 10,000 req/day
curl -X POST https://api.utilix.tech/v1/tools/regex-test \
  -H "Authorization: Bearer utx_live_..." \
  -H "Content-Type: application/json" \
  -d '{"pattern": "\\d{3}-\\d{4}", "input": "call 555-0199", "flags": "g"}'

Get an API key from your dashboard · Full API docs →

Related tools

Regex CheatsheetComplete regex reference with live pattern testerRegexHTTP Request BuilderBuild and test HTTP requests with headers, body, and authNetworkNL → Regex (AI)Describe what you want to match in plain English: get a regex pattern, explanation, and test cases powered by GPT-4o miniRegex