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Regex Tester

Test JavaScript regular expressions live. Highlight matches, inspect capture groups, toggle flags, and copy a ready-to-paste literal. All in your browser.

  • Runs in browser
  • No signup
  • No tracking
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How to use Regex Tester

  1. Enter a pattern in the regex field.

  2. Toggle flags as needed (g, i, m, s, u, y).

  3. Paste sample text — matches highlight live.

  4. Inspect capture groups in the side panel.

When to use it

  • Building input validation patterns (emails, slugs, IDs).

  • Extracting structured data from logs.

  • Search-and-replace planning before running it on real files.

  • Learning regex by experimenting safely.

What it fixes

  • Regex that 'works' until it hits an edge case in production.

  • Escape character confusion when copying patterns into JS strings.

  • Silent group-naming typos.

About Regex Tester

A regex tester is the difference between confident regex and superstition. This one uses the same engine your code does — JavaScript's `RegExp` — so what works here works in production.

Matches highlight as you type. Capture groups (numbered and named) show in a side panel. Flags toggle individually. The output gives you a copy-pastable JS literal so you don't fight escape characters when porting back to code.

References: MDN — RegExp · MDN — Regex syntax cheatsheet

Frequently asked

  • Which regex flavor is supported?

    JavaScript's native RegExp engine — same as your browser and Node.js. Lookbehind, named groups, and Unicode property escapes work in modern browsers.

  • Why doesn't my PCRE regex work?

    JS regex doesn't support some PCRE features: possessive quantifiers, recursion, backreferences inside lookbehind. Most patterns translate one-to-one.

  • What does the 'g' flag do here?

    Global flag — finds all matches instead of just the first. Required to see more than one highlight.

Discussion

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