Regex Syntax Reference

Verified 2026-09-25 Each verified example was run in JavaScript, Python re, PCRE2-8 and Go regexp, unless its card names other engines.

• Regex Anchors

  Learn how ^ and $ anchor a match, and how the m flag changes them to line starts and ends.

  ^cat$
  Open in workbench — Regex Anchors

• Regex Character Classes

  Learn how a character class matches one character from a set, with a runnable example.

  [A-F0-9]{2}
  Open in workbench — Regex Character Classes

• Regex Quantifiers

  Learn how greedy and lazy quantifiers repeat, with a runnable example.

  a+?
  Open in workbench — Regex Quantifiers

• Regex Capture Groups

  Learn how capture groups number their parts and keep values as strings.

  ([A-Z]{2})-(\d{3})
  Open in workbench — Regex Capture Groups

• Regex Named Groups

  Learn named groups and why their syntax differs between JavaScript, Python, PCRE2 and Go.

  (?<id>TX-\d{5})
  Open in workbench — Regex Named Groups

• Regex Lookaround

  Learn lookahead and lookbehind, and which engines support them.

  (?<=ID=)\d+
  JavaScript · This browserPython re · Local WASMPCRE2-8 · Local WASM
  Open in workbench — Regex Lookaround

• Regex Flags

  Learn what regex flags change, and which flags each engine accepts.

  cat
  Open in workbench — Regex Flags

• Regex Escaping

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

  \.
  Open in workbench — Regex Escaping

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