UUID v4 is a randomly generated UUID. Its bits are set using a cryptographically secure random number generator, making it statistically unique. The version field is set to 4 (the 13th character is always '4') and the variant field follows RFC 4122.

What does a UUID look like?

A UUID follows the format xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx where x is a hexadecimal digit (0–9, a–f). It is 36 characters long including the four hyphens. Example: 550e8400-e29b-41d4-a716-446655440000.

UUID v4 has 122 bits of randomness, giving 2^122 possible values (about 5.3 × 10^36). The probability of generating a duplicate is astronomically small — roughly 1 in 5.3 undecillion — making them effectively unique for all practical purposes.

Free · Client-side · RFC 4122

UUID v4 Generator

Generate cryptographically secure UUID v4 identifiers instantly — no server, no signup, no limits.

UUID v4 Generator

All UUIDs generated locally in your browser. Nothing is sent to any server.

Quantity

Version

v4 (random)

Your UUIDs will appear here.
Set a quantity and click Generate.

What is UUID v4?

A UUID v4 is a randomly generated 128-bit identifier defined by RFC 4122. Values are produced using a cryptographically secure random number generator (such as crypto.getRandomValues() in browsers), giving 122 bits of entropy. The version nibble is set to 4 and the variant bits conform to the RFC 4122 standard, ensuring an astronomically large space of unique IDs.

550e8400-e29b-41d4-a716-446655440000

Length

36 characters — 32 hex digits + 4 hyphens

Randomness

122-bit entropy — ~5.3 × 10³⁶ possible values

Standard

RFC 4122 — also ITU-T X.667 and ISO/IEC 9834-8

Overview

What is a UUID v4?

UUID version 4 is a randomly generated identifier defined in RFC 4122. Unlike other versions, v4 does not include timestamps, namespaces, or hardware addresses; instead, it uses cryptographically secure random bytes for maximum unpredictability.

Because v4 UUIDs draw from 122 bits of randomness, there are about 5.3 × 10³⁶ possible values. This makes collisions practically impossible, so you can generate them anywhere without coordination and still expect global uniqueness.

128 bits = 16 bytes of data
Represented as 32 hex digits + 4 dashes (36 chars)
Case-insensitive — upper or lowercase are equivalent
Supported natively in PostgreSQL, MySQL, MongoDB, and more

UUID Format

550e8400-e29b-41d4-a716-446655440000

550e8400 time_low
32 bits

e29b time_mid
16 bits

41d4 time_hi & version
16 bits

a716 clock_seq
16 bits

446655440000 node
48 bits

The 13th character encodes the version (e.g. 4 for v4).
The 17th character (after 3rd dash) encodes the variant.

Versions

UUID Versions Compared

There are several UUID versions, each suited to different use cases.

Version	Generation Method	Best For	Requires
v1	MAC address + timestamp	Time-ordered logging — UUID v1 Generator →	Network interface
v2	DCE Security (POSIX UID/GID)	Legacy DCE systems	System identity
v3	MD5 hash of namespace+name	Deterministic IDs from names — UUID v3 Generator →	Namespace UUID + input
v4	Cryptographically random	General purpose — most common	Nothing (this tool)
v5	SHA-1 hash of namespace+name	Deterministic IDs (secure)	Namespace UUID + input
v6	Reordered timestamp (RFC 9562)	Sortable time-based IDs	Clock + node
v7	Unix timestamp + random (RFC 9562)	Database-friendly sortable IDs	Nothing (modern standard)

Live Examples

Example UUID v4 Values Generated Today

Fresh UUID v4 examples generated client-side on page load. Click any to copy.

How It Works

How This UUID v4 Generator Works

This tool generates UUID v4 values entirely inside your browser using the Web Crypto API (crypto.getRandomValues()), which produces cryptographically secure pseudo-random numbers — the same level of randomness used in encryption.

No data leaves your device. The generation algorithm follows RFC 4122 §4.4:

Fill 16 bytes with cryptographically secure random data
Set bits 12–15 of byte 6 to 0100 (version 4)
Set bits 6–7 of byte 8 to 10 (RFC 4122 variant)
Format as xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx

Common Use Cases

UUIDs are the preferred unique identifier for:

Database primary keys REST API resource IDs Distributed systems Session tokens File naming Order & transaction IDs Message queue IDs User identifiers Microservice entities Idempotency keys Mobile device IDs Test fixture data

FAQ

Frequently Asked Questions

Concise answers about UUIDs and this generator tool.

A UUID v4 is a randomly generated 128-bit identifier used to uniquely identify information in computer systems without centralized coordination. It is standardized by IETF RFC 4122 and represented as 32 hex digits separated by hyphens into 5 groups: xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx, with the 13th character always 4. Example: 550e8400-e29b-41d4-a716-446655440000.

A UUID is 36 characters long and looks like this: 550e8400-e29b-41d4-a716-446655440000. It consists of 32 hexadecimal digits (0–9 and a–f) arranged in the pattern 8-4-4-4-12 separated by hyphens. The format is case-insensitive; uppercase and lowercase are equivalent.

UUID v4 is a randomly generated UUID. Nearly all of its 128 bits are set using a cryptographically secure random number generator, with only 6 bits reserved to encode the version (4) and variant (RFC 4122). This makes it the simplest and most widely-used UUID version for general-purpose unique IDs.

UUID v4 has 122 bits of randomness, yielding approximately 5.3 × 10³⁶ possible values. The probability of generating a single duplicate after creating 1 billion UUIDs per second for 100 years is about 50% — so for practical purposes at any real-world scale, collisions are essentially impossible.

Use UUIDs when you need unique identifiers without a central authority: database primary keys in distributed systems, API resource identifiers, session tokens, file names to avoid collisions, transaction IDs, and anywhere you need globally unique values across multiple independent systems or services. If you need time-ordered identifiers (e.g. for Cassandra or audit logs), consider our UUID v1 Generator which embeds a timestamp in each ID. If you need deterministic name-based identifiers from the same namespace and string input, use our UUID v3 Generator.

UUID and GUID refer to the same concept. GUID (Globally Unique Identifier) is the term used by Microsoft in its COM/DCOM/OLE technologies, while UUID is the IETF standard term. Both use the same RFC 4122 format and are functionally identical.

Yes. This tool uses the browser's built-in crypto.getRandomValues() API, which is cryptographically secure. All generation happens locally in your browser — no data is sent to any server, and the generated UUIDs are never logged, stored, or transmitted.

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UUID v4 Generator

UUID v4 Generator

What is a UUID v4?

UUID Format

UUID Versions Compared

Example UUID v4 Values Generated Today

How This UUID v4 Generator Works

Common Use Cases

Frequently Asked Questions

What is UUID v4?

What does a UUID look like?

What is UUID v4?

Are UUIDs truly unique?

When should I use a UUID?

What is the difference between UUID and GUID?

Is this UUID generator secure?

Complete UUID Tools Directory

UUID Generation

UUID Validation

UUID Parsing

UUID Formatting

UUID Conversion

Developer UUID Generators

Alternative ID Generators

25+ UUID & ID Tools

Explore All Free Developer Tools