UUID Generator and Validator

Tools and Utilities • Digital and Web Utilities

Written by STEM Calculators Team Published December 29, 2025 Updated February 24, 2026

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Action

Generate UUIDs (v4 by default) or validate a list (one per line).

Version

This calculator generates RFC 4122 UUID version 4.

Count

Custom count

Max recommended: 5000 for browser performance.

Format

Case

Hyphens

Wrapper

Line endings

v4 UUID layout: 8-4-4-4-12. Version is the first nibble of group 3. Variant is the first nibble of group 4.

Ready

UUID anatomy Shows groups, version nibble, and variant nibble for the selected UUID.

(Generate or validate UUIDs to see anatomy.)

Legend

Group (8-4-4-4-12)

Version nibble (UUID version)

Variant nibble (RFC 4122 variant)

For RFC 4122 UUIDs, the variant nibble is one of: 8, 9, a, b (binary 10xx).

Generated UUIDs

Copy or download the generated list.

Validation results

Valid/invalid per line + detected version/variant.

#	Input	Status	Version	Variant	Normalized
Run Validate to populate this table.

Choose Generate or Validate, then run.

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UUID Generator and Validator

A UUID (Universally Unique Identifier) is a 128-bit identifier typically written as 32 hexadecimal characters, commonly displayed in five groups separated by hyphens: 8-4-4-4-12. This calculator generates RFC 4122-compliant UUIDs (version 4 by default) and validates UUIDs you paste in.

Standard: UUID layout, versions, and variants follow RFC 4122. Version 4 UUIDs are random UUIDs defined by that same standard.

UUID text format

The most common string form is: xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx

Part	Group length	Meaning
Group 1	8 hex	Time/Random field (depends on version)
Group 2	4 hex	Time/Random field (depends on version)
Group 3	4 hex	Starts with the version nibble (`M`). For v4, that nibble is `4`.
Group 4	4 hex	Starts with the variant nibble (`N`). For RFC 4122 variant, the first nibble is one of `8`, `9`, `a`, `b`.
Group 5	12 hex	Node/Random field (depends on version)

Version and variant (the two “fixed” markers)

Even for random UUIDs, RFC 4122 requires two sets of bits to be fixed so that software can recognize the UUID type:

Version: stored in the first nibble of group 3. For v4, that nibble is 4.
Variant: stored in the first nibble of group 4. For RFC 4122 UUIDs, the two most significant bits are 10, which corresponds to hex values 8..b.

550e8400-e29b-41d4-a716-446655440000

In the example above, the version nibble is highlighted in blue, and the variant nibble is highlighted in yellow.

Generate mode (v4)

In Generate mode, the tool creates v4 UUIDs (random UUIDs). A correct v4 UUID is produced by:

Generate 16 random bytes (128 bits).
Force the version bits: set the version nibble to 0100 (hex 4) in group 3.
Force the variant bits: set the two most significant bits of the group-4 leading byte to 10, yielding a leading hex nibble of 8, 9, a, or b.
Print as hex using the 8-4-4-4-12 layout.
Apply formatting options (case, hyphens, braces, or urn:uuid: prefix).

If the browser supports it, the tool prefers crypto.randomUUID() for a direct RFC 4122 v4 UUID. Otherwise it uses crypto.getRandomValues() and then sets the required version/variant bits.

Formatting options

Option	Example output	Why it matters
Case	`550e8400-e29b-41d4-a716-446655440000` vs `550E8400-E29B-41D4-A716-446655440000`	UUIDs are case-insensitive, but some systems prefer a consistent style.
Hyphens	`550e8400e29b41d4a716446655440000`	Some APIs store UUIDs without hyphens; others expect the canonical hyphenated form.
Braces	`{550e8400-e29b-41d4-a716-446655440000}`	Often seen in Windows/registry contexts or legacy formats.
URN form	`urn:uuid:550e8400-e29b-41d4-a716-446655440000`	Used when UUIDs are represented as URNs (Uniform Resource Names).

Validate mode (one per line)

In Validate mode, the tool checks each line and reports whether it is an RFC 4122 UUID. The validator accepts several common wrappers and then normalizes the value:

Optional prefix: urn:uuid:
Optional braces: {...}
Hyphenated or non-hyphenated forms

After normalization, the tool checks:

Hex length: exactly 32 hexadecimal characters.
Variant: the variant nibble indicates RFC 4122 (8..b).
Version: reads the version nibble in group 3 and reports it as v1..v5 (or other values if present).

A UUID can have the right length and hex digits and still be invalid if its variant is not RFC 4122. That is why the tool reports both version and variant.

Validation output fields

Field	Meaning
Status	Valid if the UUID matches RFC 4122 variant rules and contains a detectable version nibble.
Version	Read from the first nibble of group 3 (example: `4` for v4).
Variant	Determined by the first nibble of group 4 (RFC 4122 corresponds to `8..b`).
Normalized	The canonical hyphenated lowercase form (useful for storing and comparing).
Reason	Shown for invalid entries (e.g., “Not 32 hex digits”, “Wrong variant”, “Empty line”).

The visualization: UUID anatomy highlight

The calculator’s visualization displays a UUID split into its five groups and highlights:

The five groups (8-4-4-4-12).
The version nibble (first hex character of group 3).
The variant nibble (first hex character of group 4).

This makes it easy to spot formatting errors (wrong group lengths) and compliance errors (wrong version/variant nibble) at a glance.

Processing steps

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