Regex Tester

Paste a pattern and some sample text, toggle the g, i, m, and s flags, and this Regex Tester shows live matches, a capture-group table, and instant syntax errors.

What is the Regex Tester?

Regex Tester is a browser-based scratchpad for regular expressions. You supply a pattern and a block of test text, and it compiles that pattern with the browser's native RegExp constructor and reports exactly what matched. Matches are highlighted inside your text, capturing groups are broken out in a table, and the status badge flips to Invalid with the engine's own error message the moment your syntax breaks.

Key Features

• Live matching as you type, with matches highlighted inside your text
• Checkboxes for the global, ignore-case, multiline, and dotAll flags
• Capture-group table listing each numbered group, non-capturing groups excluded
• Match count, group count, and instant valid or invalid status
• Copy Matches button puts every match on the clipboard, one per line

Common Use Cases

• Checking a log-scraping pattern against real log lines before wiring it into code
• Debugging a validation rule that rejects input your users insist is valid
• Pulling every ID, URL, or date out of a pasted block of text
• Learning quantifiers and anchors by watching the highlights shift as you type

How to Use the Regex Tester

1. Type or paste your pattern into the Regular Expression field, without the surrounding slashes.
2. Set the flags you need: Global (g) and Case Insensitive (i) start on, and Multiline (m) or Dot All (s) are one click away.
3. Paste realistic sample text into the Test String box, including the edge cases you expect to fail.
4. Read the Results panel to see which spans highlighted, then check the Matches, Groups, and Status badges.
5. Open the Captured Groups table to verify each group, then press Copy Matches to take the results elsewhere.

Tips for Best Results

• Strip the slashes and trailing letters when pasting a pattern; this field takes the pattern body only.
• Use lazy quantifiers between delimiters, because a greedy match keeps running to the last one.
• Turn Global off to study a single match; only the first hit is then found and highlighted.
• Avoid nested quantifiers, since backtracking can stall the tab on long near-matches.

Why Use WiserWork's Regex Tester?

Most regex debugging happens by editing code, rerunning it, and squinting at output. Here the loop is immediate, since every keystroke recompiles the pattern and repaints the highlights, so you can see precisely where a quantifier is grabbing too much. And because it runs on the browser's own engine, what you see is what your JavaScript will actually do, not an approximation borrowed from another flavor.

Who Uses the Regex Tester?

Developers building form validation, log parsers, and text-extraction scripts use it to sanity-check patterns against real samples first. Data and support teams reach for it when cleaning messy exports or hunting for a string shape in a dump. It is also a low-stakes place for anyone learning character classes, anchors, and capture groups to experiment without breaking a build.

Frequently Asked Questions

Which regex flavor does this tester use?

It compiles your pattern with the browser's built-in RegExp constructor, so you get the JavaScript (ECMAScript) flavor, the same one your front-end code and Node scripts run.

Which flags can I turn on?

Four: Global (g), Case Insensitive (i), Multiline (m), and Dot All (s). Global and Case Insensitive are on by default. There are no toggles for the unicode (u) or sticky (y) flags.

Should I paste the slashes around my pattern?

No. Enter only the pattern body and let the checkboxes supply the flags. Typed slashes become literal characters and will quietly stop the pattern from matching.

Why does my Python or PHP pattern behave differently here?

JavaScript has no atomic groups, possessive quantifiers, recursion, or the inline case-insensitive prefix that PCRE and Python accept. Its digit and word shorthands also stay ASCII-only, while Python 3 matches Unicode digits and letters by default.

What exactly do the Matches and Groups counters mean?

Matches is the number of full matches found. Groups is the total of captured groups across all of them, so a two-group pattern hitting three times reports six.

Does it show capture groups?

Yes. When your pattern has at least one capturing group, a Captured Groups table appears with the full match and each numbered group per row. Non-capturing groups never appear there, which is a good reason to use them for grouping you do not need to read back.

Can it do search and replace?

No. This tool matches, highlights, counts, and copies results; it has no replacement field and performs no substitution.

Is my test text sent anywhere?

No. The pattern and the test string stay in the page, and matching happens locally in your browser with no server request.

Why did the page hang on a long test string?

Almost certainly catastrophic backtracking. Ambiguous nested quantifiers explode combinatorially on input that nearly matches, and matching runs on the page's main thread, so rewrite the pattern to remove the ambiguity.

Can I validate email addresses with a regex here?

You can match common shapes, and the sample pattern does exactly that, but fully correct email matching is a well-known trap. Prefer a loose check plus a confirmation message over an enormous pattern.

Regex is far easier to trust when you can watch it work. Paste a pattern, paste realistic text, flip the flags, and read the highlights and the group table before that expression ever reaches production code.