Regex Generator from Examples

Build a regex from marked examples; up to three candidates are checked against your positive and negative examples.

Build a regex from marked examples

Checking engine…

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Workspace actions

Regular expression
Reference

Regex quick reference

^ · $
Start/end; m = lines.
[abc] · \d
Listed character / digit.
* · + · ?
Zero or more, one or more, optional.
(...)
Capture a numbered group.
(?<name>...)
Named capture.
(?=...)
Ahead; lookbehind varies.
i · m · s
Ignore case / line anchors / dot-newline.
Browse the full reference

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the RegExp of this browser (version not pinned)

Not available in JavaScript · This browser: x · ignore pattern whitespace; a · ASCII-only classes; U · lazy by default; J · duplicate names. u and v cannot be combined.

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Verified Fixture FX-R01

What it does

Build a regex from examples you mark yourself: at most three candidates, each checked on the selected engine against your positive and negative examples.

How to use it

  1. Paste one positive example and select the parts that vary.
  2. Declare each part: digits, letters, spaces, any characters or exact text, with its length.
  3. Add more positive and negative examples, generate, and apply a candidate only after reading its check.

Verified example

Example

Text "paid TX-00057; pending TX-00128"

JavaScript · This browser
\bTX-\d{5}\b

Result: "TX-00057", "TX-00128"

Python re · Local WASM
\bTX-\d{5}\b

Result: "TX-00057", "TX-00128"

PCRE2-8 · Local WASM
\bTX-\d{5}\b

Result: "TX-00057", "TX-00128"

Go regexp · Local WASM
\bTX-\d{5}\b

Result: "TX-00057", "TX-00128"

Counterexample

Text "TX-12"

JavaScript · This browser
\bTX-\d{5}\b

Result: no match

Python re · Local WASM
\bTX-\d{5}\b

Result: no match

PCRE2-8 · Local WASM
\bTX-\d{5}\b

Result: no match

Go regexp · Local WASM
\bTX-\d{5}\b

Result: no match

Recorded by running fixture FX-R01 on : rp.js@1 on Node v24.21.0 (V8), v24.21.0, CPython 3.14.2 (Pyodide 314.0.7), PCRE2 10.48, go1.27.1. JavaScript results come from the rp.js@1 core on Node’s V8; your browser runs the same core.

Engines

Limits