UUID Generator — Generate UUID v4 Online, Free

UUID Generator creates cryptographically random UUID version 4 identifiers using the browser's crypto.randomUUID() API. You can generate a single UUID or up to 1000 at once.

What Is a UUID and When Should You Use One?

A UUID (Universally Unique Identifier) is a 128-bit identifier standardised by RFC 4122. UUIDs are formatted as 32 hex digits grouped by hyphens: xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx, where M encodes the version and N encodes the variant. UUID v4 is the most commonly used version: 122 of the 128 bits are randomly generated, making collisions essentially impossible in practice (the probability of generating one duplicate among a billion UUIDs is about 1 in a billion billion).

UUIDs are used as primary keys in distributed databases, file names for uploaded assets, correlation IDs in distributed tracing, idempotency keys in payment APIs, and identifiers in any system where you need a unique ID without a central coordinator. They are preferred over auto-incrementing integers when: records are created on multiple machines simultaneously, the ID must not reveal the number of records, or records are merged from multiple databases.

UUID Versions Explained

v1 UUIDs embed a timestamp and the generating machine's MAC address, making them sortable by creation time. However, embedding the MAC address raises privacy concerns — it identifies the machine. v3 and v5 are namespace-based deterministic UUIDs generated by hashing a namespace UUID and a name (MD5 for v3, SHA-1 for v5) — the same namespace+name always produces the same UUID, useful for creating stable identifiers for known entities. v4 is purely random. The newest v6, v7, and v8 (RFC 9562) bring sortability back without the MAC address: v7 uses a Unix timestamp milliseconds prefix, making UUIDs database-index-friendly like ULIDs.

If you need sortable IDs for a database, consider the ULID Generator instead of UUID v4. ULIDs sort lexicographically by creation time, which keeps database B-tree indexes efficient and avoids index fragmentation — a significant performance issue with random UUID v4 primary keys at scale.

Common Use Cases

Generating unique identifiers for database records
Creating correlation IDs for distributed system tracing
Generating UUIDs for test data fixtures
Creating unique IDs for feature flags or A/B test variants

Frequently Asked Questions

What is a UUID v4?

A UUID (Universally Unique Identifier) version 4 is a 128-bit number generated using random or pseudo-random numbers, formatted as xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx. The v4 variant has extremely low collision probability.

How is a UUID different from a ULID?

UUIDs are random and do not sort chronologically. ULIDs (Universally Unique Lexicographically Sortable Identifiers) embed a millisecond timestamp prefix, so they sort by creation time and are database-index-friendly.

Privacy & Security

This tool runs entirely in your browser using client-side JavaScript. No data is sent to a server — your input never leaves your machine. SmartDevBox has no account system, no usage tracking, and no paid tier. See the Privacy & Security page for full details.

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