UUID Generator

How to generate a UUID

1. Select a version: choose v4 for a purely random UUID or v7 for a time-sorted UUID suited to database primary keys.
2. Generate: click Generate (or set a count up to 10,000 and generate in bulk). Each UUID is created using your browser's cryptographically secure random number generator, no server involved.
3. Copy: click Copy All to grab every UUID, or export as a JSON array, CSV, or SQL VALUES clause and paste directly into your code or database seed script.

UUID v4 vs v7: which to use in 2026

v4 is 122 bits of pure randomness plus 6 version/variant bits, no timestamp component whatsoever. That makes it ideal for user IDs, session tokens, API keys, and any opaque identifier where sequential order must not leak. The downside: random insertion order destroys B-tree locality in databases, causing page splits and slower index scans on write-heavy tables.

v7 (RFC 9562, ratified 2024) embeds a 48-bit Unix millisecond timestamp in the first 48 bits, followed by random bits. Lexicographic sort equals time sort. Use v7 for database primary keys in PostgreSQL, MySQL, MongoDB, and any write-heavy table where chronological sort order matters. Index performance is dramatically better than v4 because rows insert in roughly sequential order. Most new schemas in 2026 default to v7. See the deep-dive: UUID v4 vs v7 for databases.

v1 encodes your MAC address and a timestamp, a privacy risk; avoid it in public-facing systems.

v8 is reserved for custom/experimental formats and is not intended for general use.

UUID format

A UUID is always 32 hexadecimal digits arranged in five groups separated by hyphens, totalling 36 characters:

xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx

• M: the version digit. 4 for v4, 7 for v7.
• N: the variant bits. Always 8, 9, a, or b for RFC 9562 UUIDs.

Example (v4):

550e8400-e29b-41d4-a716-446655440000

The format is identical whether you call them UUIDs (IETF) or GUIDs (Microsoft), the 36-character string is the same. Some systems strip hyphens for a compact 32-char hex form; others wrap in braces ({550e8400-...}) for .NET Guid compatibility. This tool supports all three output styles.

UUID collision probability

UUID v4 has 122 random bits, giving 2¹²² possible values, approximately 5.3 × 10³⁶ unique UUIDs. To put that in perspective:

• At 1 trillion (10¹²) generated UUIDs, the probability of any collision is roughly 1 in 10¹²: one in a trillion.
• To reach a 50% chance of collision you would need to generate around 2.7 × 10¹⁸ UUIDs: more than the estimated number of grains of sand on Earth.

For practical purposes: you will never see a UUID collision in production. The birthday-paradox math only becomes relevant at astronomical scale. Read the full analysis: UUID collision probability explained.

UUID in different languages

Every major runtime ships native UUID generation. No third-party library needed in most cases:

JavaScript / TypeScript (Node.js 19+ and all modern browsers)

// Native, no library needed
crypto.randomUUID() // returns a v4 UUID string

Python

import uuid

str(uuid.uuid4())   # v4 random UUID
str(uuid.uuid7())   # v7 time-sorted UUID (Python 3.14+)

Go

import "github.com/google/uuid"

uuid.New().String()        // v4
uuid.Must(uuid.NewV7()).String() // v7

PHP

// PHP 8.3+
$uuid = \Symfony\Component\Uid\Uuid::v4()->toRfc4122();
// or composer require ramsey/uuid
\Ramsey\Uuid\Uuid::uuid4()->toString();

SQL (PostgreSQL 13+)

SELECT gen_random_uuid(); -- v4, built-in, no extension needed

When to use a UUID (and when not to)

• Use UUID: distributed system primary keys (no coordination needed), public-facing IDs where sequential enumeration would be a security risk, idempotency keys, request trace IDs.
• Skip UUID: human-readable slugs (my-blog-post beats 01928f9c-9e42-7d3f-...), monotonic counters where you need guaranteed ordering without timestamp coupling, storage-constrained environments (128 bits vs. 64-bit integer). For those cases consider a password generator for secrets or a hash generator for content-addressed IDs: note that hashes and UUIDs serve different purposes: hashes are deterministic, UUIDs are not.
• UUID vs ULID: ULIDs are also time-sortable but use base32 encoding and are 26 characters instead of 36: shorter and URL-safe by default. UUIDs have broader ecosystem support. Read the comparison: NanoID vs UUID.

Related articles

• 4 min readCUID2: Collision-Resistant IDs Better Than UUID v4CUID2 generates secure, URL-safe, database-friendly IDs with better collision resistance than UUID v4. Learn how CUID2 differs from UUID, nanoid, and ULID, with JavaScript and...
• 4 min readUUID Versions Explained: v1, v3, v4, v5, and v7UUID has multiple versions with different generation strategies. Learn when to use UUID v4 (random), v5 (name-based SHA-1), v7 (time-ordered), and why v1 and v3 are largely...
• 5 min readNanoID vs UUID: Which Unique ID Generator Should You Use?NanoID generates shorter, URL-safe unique IDs using a custom alphabet. UUID v4 is the standard 128-bit identifier. Here's when to use each and how they compare on size, speed,...
• 5 min readULID Generator: Universally Unique Lexicographically Sortable IdentifiersULID is a 26-character sortable unique identifier that embeds a millisecond timestamp prefix. Unlike UUID v4, ULIDs sort chronologically. Here's how ULIDs work and when to use...
• 5 min readUUID Collision Probability: How Likely Are Duplicate UUIDs?UUID v4 has 122 bits of randomness. Collisions are theoretically possible but astronomically unlikely. Here's the math behind UUID uniqueness and when collision risk actually...
• 5 min readUUID Format: Understanding the 128-Bit Unique Identifier StructureUUIDs follow a specific 8-4-4-4-12 hexadecimal format defined by RFC 4122. Here's what each section of a UUID means, the version and variant bits, and how to parse UUID fields.
• 5 min readUUIDs in Databases: Performance, Storage, and Best PracticesUUIDs as primary keys have real performance implications in PostgreSQL and MySQL. Learn UUID storage size, index fragmentation with random UUIDs, why UUID v7 is better than v4...
• 5 min readUUID v4 Generator: Random UUIDs ExplainedUUID v4 uses random bits to generate universally unique identifiers. Here's how v4 differs from other UUID versions, what makes them unique, and when to use UUID v4 vs...
• 8 min readUUID v4 vs v7 for Databases: The Benchmark You NeedUUID v4 fragments your primary key index. UUID v7 fixes it with millisecond-ordered timestamps. Here's the benchmark data, why it matters, and when to switch.

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