Generate and Manage UUIDs
A UUID (Universally Unique Identifier) is a 128-bit value used to identify something — a database record, a session, a file, an event — without needing a central authority to hand out the next number in sequence. This tool generates version 4 UUIDs, the random variant defined by RFC 4122, using the browser's Web Crypto API for genuinely cryptographically secure randomness.
Click the refresh icon for a new UUID, or copy the one already shown. Each one is a 32-character hexadecimal string split into five groups by hyphens, and the odds of two independently generated UUIDs colliding are astronomically small.
How is a UUID v4 generated?
A UUID v4 is built from 122 random bits — the remaining 6 bits are fixed to mark the
version (4) and variant, which is why every UUID this tool produces has a "4" in the same
position and starts its next group with 8, 9, a, or b. This tool uses
crypto.randomUUID(), the browser's native, spec-compliant implementation, so
there's no custom randomness logic to get wrong.
What are UUIDs actually used for?
Databases use them as primary keys so records stay unique even when merging data from multiple sources. Distributed systems use them to generate IDs on separate machines without coordinating with each other first. They also show up as session tokens, file names, log event IDs, and test fixture data — anywhere a guaranteed-unique identifier matters more than a short or sequential one.
Why not just use an incrementing number?
A sequential ID (1, 2, 3…) only stays unique within a single database or system. The moment you merge two databases, run multiple services that each create their own records, or let a client generate an ID before it reaches the server, sequential numbers collide. A randomly generated UUID doesn't have that problem — it can be created anywhere, by anyone, with no coordination, and still be unique.
Related tools
- Strong Password Generator — the same cryptographically secure randomness, shaped into a usable password.
- Random Number Generator — for everyday randomness (games, raffles) that doesn't need cryptographic security.
Last reviewed: August 2026