Question 1

What does the UUID v4 regex pattern do?

Accepted Answer

Matches UUID v4: 8-4-4-4-12 hex digit groups separated by hyphens. The version nibble (position 13) must be 4, and the variant nibble (position 17) must be 8, 9, a, or b.

Question 2

How do I use the UUID v4 regex in JavaScript?

Accepted Answer

Use the pattern /[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}/gi with the String.match() or String.matchAll() method. For example: const matches = text.match(/[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}/gi);

Question 3

What regex flags does this pattern use?

Accepted Answer

This pattern uses the global, case-insensitive flags (gi). The global flag finds all matches in the input, not just the first. The case-insensitive flag matches regardless of letter casing.

Question 4

Which programming languages support this regex?

Accepted Answer

Fully supported in JS, PYTHON, JAVA, PHP, GO, RUBY, CSHARP

Question 5

What strings does this regex match?

Accepted Answer

This pattern matches strings like: 550e8400-e29b-41d4-a716-446655440000, 6ba7b810-9dad-41d1-80b4-00c04fd430c8. It does not match strings like: 550e8400-e29b-31d4-a716-446655440000, not-a-uuid, 550e8400e29b41d4a716446655440000.

Question 6

When should I use the UUID v4 regex?

Accepted Answer

Use this pattern to validate UUID v4 identifiers in API requests, database records, or configuration files. UUID v4 is the most common version, generated from cryptographically random numbers (RFC 4122). If you need to match any UUID version (v1 through v5), use the 'Any version' variation instead. For generating UUIDs, use crypto.randomUUID() in JavaScript or uuid.uuid4() in Python rather than building them with regex.

Question 7

What are common mistakes with the UUID v4 regex?

Accepted Answer

A common mistake is: Not checking the version nibble — using [0-9a-f]{4} for the third group. Instead, use 4[0-9a-f]{3} because The third group's first character must be '4' for UUID v4. Without this check, the pattern matches UUIDs of any version (v1, v3, v5, etc.).. A common mistake is: Not checking the variant nibble — using [0-9a-f]{4} for the fourth group. Instead, use [89ab][0-9a-f]{3} because The fourth group's first character must be 8, 9, a, or b per RFC 4122. Without this, the pattern accepts non-standard UUID variants.. A common mistake is: Forgetting case insensitivity when matching UUIDs. Instead, use Use the i flag or include A-F in character classes because UUIDs are often represented in uppercase (550E8400-E29B-...) or mixed case. The i flag ensures both cases match.

Question 8

How does the UUID v4 regex work step by step?

Accepted Answer

`[0-9a-f]{8}` — Match 8 hexadecimal characters — the time-low field. `-` — Match a literal hyphen separator. `[0-9a-f]{4}` — Match 4 hex characters — the time-mid field. `-` — Match a literal hyphen separator. `4[0-9a-f]{3}` — Match the version nibble '4' followed by 3 hex characters — identifies this as UUID version 4. `-` — Match a literal hyphen separator. `[89ab][0-9a-f]{3}` — Match the variant nibble (8, 9, a, or b) followed by 3 hex characters — indicates the RFC 4122 variant. `-` — Match a literal hyphen separator. `[0-9a-f]{12}` — Match 12 hex characters — the node field (typically random in v4)

Token	Explanation
`[0-9a-f]{8}`	Match 8 hexadecimal characters — the time-low field
`-`	Match a literal hyphen separator
`[0-9a-f]{4}`	Match 4 hex characters — the time-mid field
`-`	Match a literal hyphen separator
`4[0-9a-f]{3}`	Match the version nibble '4' followed by 3 hex characters — identifies this as UUID version 4
`-`	Match a literal hyphen separator
`[89ab][0-9a-f]{3}`	Match the variant nibble (8, 9, a, or b) followed by 3 hex characters — indicates the RFC 4122 variant
`-`	Match a literal hyphen separator
`[0-9a-f]{12}`	Match 12 hex characters — the node field (typically random in v4)

Language	Support
JS	Full support
PYTHON	Full support
JAVA	Full support
PHP	Full support
GO	Full support
RUBY	Full support
CSHARP	Full support

UUID v4

Pattern

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Step-by-Step Breakdown

Common Mistakes

Test Strings

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Non-matching

Language Compatibility

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Common Variations

Any version

Related Patterns

UUID (Any Version)

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