Generate UUIDs online
UUIDs (universally unique identifiers) are used everywhere in software — database keys, API request IDs, session tokens. This tool generates cryptographically random UUID v4 values using your browser's built-in Web Crypto API (crypto.randomUUID), so there's nothing to install and nothing sent over the network. Generate one at a time or a batch, then copy individually or all at once.
What version 4 means
UUID v4 is randomly generated, as opposed to v1 which encodes a timestamp and MAC address, or v5 which hashes a namespace and name. Version 4 is the right default for general-purpose identifiers because it leaks no information about when or where it was created — a v1 UUID reveals the generating machine's network address and the moment of creation, which is occasionally a genuine privacy problem.
Why collisions are not a practical concern
A v4 UUID contains 122 random bits, which is about 5.3 undecillion possible values. To reach even a one in a billion chance of a single collision you would need to generate roughly a hundred billion UUIDs. For any realistic application the probability is not worth engineering around, which is the entire point of the format — you can generate identifiers independently on many machines without coordination.
Cryptographically random, and a database caveat
These come from crypto.randomUUID, which draws on the same secure random source as other cryptographic operations rather than Math.random. One practical note if you are using UUIDs as database primary keys: their randomness means inserts scatter across the index rather than appending, which can hurt write performance on large tables. Some teams use time-ordered variants like UUIDv7 for that reason.
Frequently asked questions
- What version of UUID does this generate?
- UUID v4 — randomly generated identifiers, the most common type for general-purpose unique IDs.
- How random are these?
- They're generated using the Web Crypto API's cryptographically secure random number generator, built into your browser.
- Is there a chance of duplicates?
- UUID v4 has 122 random bits — the odds of a collision are astronomically small, even across billions of generated IDs.
- Are the UUIDs sent to a server?
- No, generation happens entirely in your browser. Nothing is transmitted.
- Can two generated UUIDs ever be the same?
- Theoretically yes, practically no. With 122 random bits you would need to generate around a hundred billion before reaching a one-in-a-billion collision chance.
- Are these suitable as database keys?
- Yes, though their randomness scatters index inserts and can slow writes on very large tables. Time-ordered variants like UUIDv7 address that.