UUID v4 Regex

Extraction

Regular expression

/^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/

Pattern breakdown

Part	Meaning
`Anchor or context`	Use anchors when you need whole-string validation.
`Main token`	The core token sequence describes the accepted text shape.
`Character class`	Character classes limit which characters are valid.
`Quantifier`	Quantifiers control how many characters or groups are accepted.
`Flags`	Use language-specific flags such as i, m, or u only when needed.

Should match

550e8400-e29b-41d4-a716-446655440000

Should not match

not-a-uuid
not matching sample
550e8400-e29b-41d4-a716-446655440000 invalid
not-a-uuid550e8400-e29b-41d4-a716-446655440000

Test cases

Input	Expected	Why it matters
`550e8400-e29b-41d4-a716-446655440000`	Match	Representative valid input for this pattern.
`not-a-uuid`	No match	Common invalid or boundary input.
`(empty string)`	No match	Common invalid or boundary input.
`not matching sample`	No match	Common invalid or boundary input.
`550e8400-e29b-41d4-a716-446655440000 invalid`	No match	Common invalid or boundary input.
`not-a-uuid550e8400-e29b-41d4-a716-446655440000`	No match	Common invalid or boundary input.

JavaScript

const re = /^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/;
re.test(input);

Python

import re
bool(re.search(r"^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$", text))

PHP

$ok = preg_match('/^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/', $value) === 1;

Java

Pattern pattern = Pattern.compile("^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$");
pattern.matcher(value).find();

Go

re := regexp.MustCompile(`^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$`)
ok := re.MatchString(value)

Notes and production use

UUID v4 regex is useful as a practical starting point. Test it against your real input, avoid using it as the only security control, and prefer a parser when the format has complex grammar.

Performance tip: avoid running complex regular expressions repeatedly on very large untrusted strings without limits. Prefer anchored validation patterns, cap input length before matching, and use a parser when the target format has nested grammar.

UUID v4