UUID Generator
Generate random version 4 UUIDs, one or many at a time.
About this tool
Generates random version 4 UUIDs in your browser using crypto.getRandomValues, the cryptographically secure random source. Set how many you need, optionally drop the hyphens or switch to uppercase, and copy the lot.
What a UUID is. A UUID (universally unique identifier), also called a GUID, is a 128-bit value written as 32 hexadecimal digits in the pattern 8-4-4-4-12, for example f47ac10b-58cc-4372-a567-0e02b2c3d479. The point is that any two parties can generate them independently, with no coordination, and still never collide in practice.
Version 4 specifically. The UUID standard (RFC 4122, updated by RFC 9562) defines several versions. Version 4 is almost entirely random: 6 bits are fixed to mark the version and variant, and the other 122 bits come from the random source. Other versions encode a timestamp and node (v1), a hash of a name (v3/v5), or a time-ordered layout (v7) — v4 is the right default when you just need an opaque unique key.
How unique is "unique"? With 122 random bits, you would need to generate roughly 2.7 × 1018 UUIDs before the chance of a single collision reaches 50% (the birthday bound). At a billion per second that's about 85 years. For any realistic application the collision risk is zero.
Formatting notes. The canonical form is lowercase with hyphens. Removing the hyphens gives a 32-character string some databases and filenames prefer; uppercase is accepted by parsers but non-canonical. All three represent the same value. UUIDs are not secret — they're identifiers, not tokens — so don't use one as a password or an access key.
v4 vs. v7 for database keys. Random v4 keys scatter inserts across a table's index, which can hurt write performance and locality on large tables. The newer v7 UUIDs are time-ordered, so recent rows cluster together. If you control the schema and insert volume is high, v7 is worth a look; v4 remains fine for most uses and for anything client-generated.
For a hash-based identifier derived from content rather than random bits, use the hash generator. For random passwords from the same secure source, see the password generator.
Frequently asked questions
- What does "version 4" mean?
- It's the all-random UUID type. The version and variant bits are fixed by the standard; the remaining 122 bits are generated from a random source rather than a timestamp or hardware address.
- How unique are these really?
- With 122 random bits, you could generate a billion per second for decades before a collision became statistically likely. In practice the risk is nil.
- Why would I remove the hyphens?
- Some databases, keys, and filenames prefer a single unbroken 32-character hex string. It's the same value without the four dashes.
- Is a UUID secret or secure to use as a token?
- No. A UUID is an identifier, not a credential. It may appear in logs and URLs. Use a proper random token for anything that grants access.
- Should I use v4 or v7 for a primary key?
- v4 is fine for most cases and for client-generated IDs. v7 is time-ordered, which improves index locality for high-volume inserts on large tables.
- Are these generated locally?
- Yes. Nothing is sent anywhere — they're produced in your browser with its built-in secure RNG.