🆔 UUID Generator & Decoder

Generate UUID v4 (pure random) or UUID v7 (time-ordered), up to 200 at a time, and paste an existing one to see what is actually inside it. The random bytes come from crypto.getRandomValues — your operating system’s generator — and never leave the tab.

Decode a UUID

Case never matters: UUIDs are hexadecimal, and A and a are the same digit.

v4 or v7?

v4 is 122 random bits with a version and variant marker. It is the right default for identifiers that must not reveal anything: two v4 UUIDs are unrelated, and neither says when it was made or by whom. v7 puts a 48-bit Unix millisecond timestamp in front, so the strings sort in creation order — useful for database keys and logs, because new rows land at the end of the index instead of scattering through it. The trade is honesty: a v7 tells anyone holding it roughly when it was created, and it leaves 74 random bits, not 122.

Both are generated the same way here — fresh bytes from the OS, then the version and variant bits overwritten — with no counter and no shared state. The practical difference for sorting is that two v7s created inside the same millisecond fall back to their random bits, so their order among themselves is arbitrary. That is also true of most libraries; a strictly monotonic sequence needs a dedicated counter, which is a database feature, not a UUID feature.

What a UUID is not

It is an identifier, not a password, a reset token or an API secret. A v4 has plenty of entropy for identity, but a secret also has to be unguessable and revocable and never logged — which is a job for a purpose-built token. A v1 UUID is the worst case of all: it embeds the machine’s MAC address and a clock, so publishing one can leak hardware and timing information. The decoder above reports exactly which of these you are holding.

Part of Everyday Tools. Need a password rather than an identifier? The password generator explains its entropy too.