Regex Parser & Tester

Test a regex against your text in the engine it will run in; everything runs in this browser.

Matches and captures in a real engine

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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No regex yet.

⋯

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.

To run: enter a regex; enter a test text.

Try a verified example

More examples (9)

Extract fields

Find and validate

Split text

Verified 2026-09-25 · rp.js@1 on Node v24.21.0 (V8); browser version varies.

Test text

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No text yet.

No result yet

Results appear here after a run.

Verified Fixture FX-R01

What it does

Check what a regular expression matches in the engine it will run in: every match, every capture group, and whether the run completed.

How to use it

  1. Type or paste the regex.
  2. Paste the text to test; add more texts with Add text.
  3. Results appear as you type; press Ctrl/Cmd+Enter to run with the longer deadline.
  4. Open Explanation or Structure to see how the pattern is read; open Code to get a program that reproduces the result.

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