RegEx Builder: Interactive Pattern Editor

Build a regular expression interactively. Type a pattern and get autocomplete suggestions; select text below to get pattern suggestions for it; matches and groups are color-coded in both the pattern and the test text, using the same color for each. Runs entirely in your browser.

Explanation

Replace

Common patterns

Export as code

Flag semantics don't map 1:1 across languages (e.g. JavaScript's g flag has no direct equivalent elsewhere, it's a different function call, not a flag). This is a reasonable starting point, not a guarantee of identical behavior, always test against your target language's actual engine.

FAQ

Why does the pattern breakdown use colors? Each capturing group gets its own color, used consistently in the pattern breakdown, the explanation list, and the highlighted matches below, so you can see at a glance which part of your pattern produced which part of the match.

How do the autocomplete suggestions work? They're based on common regex patterns (e.g. after typing \, common escape sequences are suggested; after a matchable token, quantifiers are suggested), a heuristic, not an exhaustive grammar, so it won't catch every situation.

What does "select text for suggestions" do? Selecting a substring in the test string analyzes it (all digits? letters? looks like an email or date?) and offers regex snippets that would match similar text, plus the exact literal as a fallback.

How is this different from the RegEx tester?

The RegEx tester is a straightforward "does this pattern match this text" tool with a full syntax reference. This builder is for the harder case: constructing a pattern you do not yet know how to write. It explains each token as you type, colour-codes capture groups so you can see which part of the pattern produced which part of the match, and suggests patterns from selected sample text.

Why build patterns incrementally?

A regular expression that fails gives no indication of which part is wrong. Building up a token at a time and watching the highlighting after each addition localizes the mistake immediately, which is considerably faster than staring at a finished pattern that matches nothing.

Is the generated code ready to paste?

Nearly. The pattern itself transfers correctly, but flag semantics differ between engines, and features like lookbehind have varying support. Test against your target engine before relying on it, particularly for anything security-related.

Is my test string sent anywhere?

No. Everything runs in your browser using the native RegExp engine, so testing patterns against real log excerpts or production data is safe.

Related tools