RFC 9562 Aligned · Multiple UUID Versions

UUID Generator

Generate random UUIDs instantly — v1, v3, v4, v5, v6, v7, v8, Nil, and Max (UUID v2 is not offered). Bulk export, validate, and decode. Runs entirely in your browser — your random UUID generator with zero server calls.

Only need one version? Try the dedicated UUID v4 or UUID v7 generator.

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The Basics

What is a UUID?

A UUID (Universally Unique Identifier), also called a GUID (Globally Unique Identifier) in Microsoft/.NET contexts, is a 128-bit identifier used to label for any resource — a database row, API object, session, or file — without any central authority handing out IDs. Systems can create UUIDs independently with an extremely low risk of accidental duplication when a suitable generation method is used.

Every UUID is 32 hexadecimal digits in an 8-4-4-4-12 pattern — 36 characters total:

f47ac10b-58cc-4372-a567-0e02b2c3d479

RFC 4122 (2005) introduced versions 1–5. RFC 9562 (May 2024) superseded it and formally added v6, v7, and v8. You will also see the term GUID (Globally Unique Identifier) in Microsoft/.NET contexts — it is the same standard with a byte-order difference in some implementations.

Microsoft / .NET / COM
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Version Guide

Which UUID version should you use?

UUID v7 (UUIDv7) is now the recommended default for database primary keys — it embeds a millisecond Unix timestamp so IDs sort by creation time and index far more efficiently in a B-tree than a random ID. PostgreSQL 18 ships native uuidv7() support. UUID v4 (UUIDv4, uuid4) remains a good choice for randomly generated identifiers when you do not want to expose creation time. For passwords, API credentials, and authentication secrets, use a purpose-built CSPRNG token instead. Need a new GUID instead? Select v4 above — a GUID and a UUID v4 are the same 128-bit random identifier.

VersionBased OnTime-SortableBest ForStatus
v1Timestamp + clock sequence + node (MAC or random)PartiallyLegacy distributed systemsAvoid (MAC leak)
v3Namespace + name (MD5)NoDeterministic IDs, legacyUse v5 instead
v4122 bits randomNoRandom IDs and GUIDs (UUIDv4, uuid4)Recommended
v5Namespace + name (SHA-1)NoDeterministic, reproducible IDsRecommended
v6Reordered v1 timestamp + clock sequence + nodeYesv1 migration pathRFC 9562
v7Unix ms timestamp + randomYesTime-sortable database identifiers (UUIDv7, uuid7)Recommended 2026
v8Custom layoutDependsApplication-defined schemasExperimental
Nil / MaxAll-zero / all-F—Placeholders and testingSpecial values

v1, v3, v4, and v5 appeared in RFC 4122 (2005); v2 is a DCE Security UUID defined separately. RFC 9562 is the current UUID specification. v6, v7, and v8 defined in RFC 9562 (May 2024).

Use Cases

What are UUIDs used for?

UUIDs are useful anywhere a system needs low-collision-risk identifiers without central coordination — the foundation of modern distributed software. Microsoft GUIDs generally use the same 128-bit UUID format, although not every random ID is a UUID.

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Database Primary Keys

Unique row identifiers that work across shards and replicas without a shared sequence generator.

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API Resource IDs

REST and GraphQL object identifiers that do not expose sequential counts to clients.

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Distributed Systems

Microservices and offline-first apps can generate IDs independently with no database round-trip.

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Session Tracking

Session record identifiers, request IDs, and trace IDs across logs and distributed tracing systems. Use dedicated secure tokens for authentication.

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File Naming

Low-collision-risk names for uploads and generated files; storage bucket names may need additional provider-specific rules.

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Test & Mock Data

Useful placeholder IDs and database seed data; deterministic tests may require fixed seed values.

Collision Probability

How unique is a UUID, really?

A UUID v4 has 122 bits of actual randomness. That gives roughly 5.3 × 10³⁶ possible values.

5,316,911,983,139,663,491,615,228,241,121,378,304
Possible UUID v4 values. UUID v4 offers 122 random bits. At roughly 2.7 quintillion generated UUIDs, the birthday-paradox collision probability approaches 50%.

Practically speaking, treat v4 collisions as a non-event at any realistic scale. One important caveat: a UUID is not a cryptographic secret. It is built for uniqueness, not unguessability under attack. Never use a UUID alone as an auth token or password.

Developer Reference

Generate a UUID in your language

Every major language has a native implementation to get a UUID, create a random ID, or build a unique ID generator into your own app:

Python JavaScript Java Node.js / npm PHP Go (Golang) C# / .NET TypeScript Bash / Linux Rust PostgreSQL MySQL
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This Online UUID Generator Runs Entirely in Your Browser

UUIDs generated here are processed locally in the browser using Web Crypto APIs. Random versions use your browser’s built-in crypto.getRandomValues(). The generator does not intentionally send generated UUIDs to our server. No account is required. Other site resources may still make normal network requests.

FAQ

Frequently asked questions

UUIDs are used anywhere a system needs a unique identifier without coordinating with a central authority — database primary keys, API resource IDs, session tokens, distributed event IDs, file names, and message queue IDs are the most common applications.
They are the same 128-bit identifier standard. GUID (Globally Unique Identifier) is the term Microsoft uses in .NET, COM, and Windows implementations. Some Microsoft implementations differ in byte-order representation, but for practical purposes the terms are interchangeable.
Use UUID v7 for new database primary keys — it is time-sortable and B-tree friendly. Use UUID v4 for random identifiers; use a dedicated secure token generator for authentication secrets. Avoid v1 for user-facing projects because it embeds the generating machine’s MAC address.
Yes. UUID v4 has 2^122 possible random values, so collisions are extremely unlikely with sound randomness but cannot be ruled out. The birthday-paradox probability reaches about 50% around 2.7 × 10^18 generated UUIDs.
No. UUIDs primarily identify resources; generating unpredictable authentication tokens has additional security requirements. Do not use it as a standalone password, API secret, or auth token. Use a dedicated secret generator for anything that must be unguessable under adversarial conditions.
Yes. The implemented versions follow RFC 9562, which superseded RFC 4122 in May 2024 and defines the current layouts for v1 through v8, Nil, and Max. Web Crypto supplies random bytes where the version requires randomness.
Yes — click Bulk Generate to create up to 1,000 UUIDs at once and export them as plain text, JSON, or CSV.
A UUID is 32 lowercase hexadecimal digits in five groups separated by hyphens: 8-4-4-4-12. It is always 36 characters including hyphens, or 32 without. In a hyphenated UUID, the version digit is character 15 and the variant begins at character 20 (counting from 1).

Explore More Tools

Related UUID & GUID Tools

Need something specific? Each tool below is purpose-built for a distinct use case — from GUID generation for .NET developers to bulk exports for database seeding.