UUID Generator

Frequently Asked Questions

Are UUID v4 values truly unique?

With 122 random bits, the probability of a collision is approximately 1 in 5.3 × 10^36. For any practical application generating billions of UUIDs, the collision risk is safely ignorable.

What is the difference between UUID and GUID?

GUID is Microsoft's name for the same concept. The format and structure are identical to UUID version 4. The terms are interchangeable.

Should I use UUID v4 or UUID v7?

UUID v7 uses a timestamp prefix, making new UUIDs sort after old ones and dramatically improving database index performance. For new systems with high write volumes, UUID v7 is generally preferred.

Can I use these as security tokens?

UUIDs are generated with a cryptographic source but are not secrets on their own. For security tokens, prefer signed JWTs or token formats that include audience, expiry, and a signature.

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How It Works

A UUID (Universally Unique Identifier) - also called a GUID in Microsoft terminology - is a 128-bit value typically written as 32 hexadecimal digits arranged in five groups separated by hyphens: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx (8-4-4-4-12 characters). This generator creates version 4 UUIDs, where the vast majority of bits are cryptographically random.

Version 4 UUIDs have two fixed fields: the version nibble (always 4) in the third group, and the variant bits (10xx) at the start of the fourth group. Everything else is random, giving 122 bits of randomness. The generator uses crypto.randomUUID() when available, falling back to crypto.getRandomValues() for 16 random bytes with manual bit-setting. Both sources are cryptographically strong.

Use Cases

UUIDs are used as unique identifiers in a wide range of systems:

Generating primary keys for database records when you need globally unique identifiers that can be created without coordinating with the database

Creating idempotency keys for API requests to safely retry operations without side effects

Assigning correlation IDs to distributed trace spans for logging and observability

Generating unique filenames for uploaded assets to prevent collisions and avoid exposing sequential IDs

Creating session tokens or request IDs when a unique identifier is needed but security is handled separately

Tips

UUID v4 is random, not sequential. If you need IDs that sort in insertion order, consider UUID v7 (timestamp-based, widely supported as of 2024) or ULID instead.

Store UUIDs as 16-byte binary (UUID type in PostgreSQL, MySQL, SQL Server) rather than as a 36-character VARCHAR string; binary storage cuts index size and comparison speed significantly.

UUID v4 values are not secret - they're only unique, not unguessable. Don't use a UUID alone as an authorization token; pair it with a signature or use a proper token format like JWT.

The standard textual form is lowercase; many databases and APIs compare UUIDs case-insensitively, but normalize to lowercase to avoid subtle bugs.

On modern hardware, generating millions of UUID v4 values per second is easily achievable - the randomness source is not a performance bottleneck for most applications.

FAQ

Are UUID v4 values truly unique?

With 122 random bits, the probability of any two UUID v4 values colliding is approximately 1 in 5.3 × 10^36. For any practical application generating billions of UUIDs, the collision risk is astronomically small and safely ignorable.

What is the difference between UUID and GUID?

GUID (Globally Unique Identifier) is Microsoft's name for the same concept. The format and structure are identical to UUID version 4. The terms are interchangeable for the random 128-bit identifier format described here.

Should I use UUID v4 or UUID v7?

UUID v7 uses a millisecond timestamp prefix, making new UUIDs sort lexicographically after old ones. This dramatically improves database index performance (fewer page splits, better locality) compared to random v4 UUIDs. For new systems with high write volumes, UUID v7 is generally preferred. UUID v4 remains common for compatibility and simplicity.

Can I use these as security tokens?

UUIDs are generated with a cryptographic random source (Web Crypto API), making them suitable as opaque identifiers. However, they are not secrets on their own - never use a UUID alone as the only check for authorization. For security tokens, prefer signed JWTs or purpose-built token formats that include audience, expiry, and signature.

UUID Generator

Frequently Asked Questions

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