Regex Escaping

Learn how to escape special characters, and why JSON source needs a second backslash.

Checking engine…

Not saved: closing this tab loses your work. Save keeps the regex, flags, engine, texts and tests in this browser only.
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

Tab inserts a tab · press Esc, then Tab, to leave the editor

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.

Test text

Tab inserts a tab · press Esc, then Tab, to leave the editor

No text yet.

No result yet

Results appear here after a run.

Verified Fixture FX-S08

What it does

A backslash makes a special character literal: \. matches a dot. Source code strings add their own escaping layer.

How to use it

  1. Load the example.
  2. Paste the JSON string "\\." into the regex box and accept the conversion to see the decoded pattern.
  3. Check the counterexample.

Verified example

Example

Text "a.b"

JavaScript · This browser
\.

Result: "."

Python re · Local WASM
\.

Result: "."

PCRE2-8 · Local WASM
\.

Result: "."

Go regexp · Local WASM
\.

Result: "."

Counterexample

Text "abc"

JavaScript · This browser
\.

Result: no match

Python re · Local WASM
\.

Result: no match

PCRE2-8 · Local WASM
\.

Result: no match

Go regexp · Local WASM
\.

Result: no match

Recorded by running fixture FX-S08 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