Security

UUID Generator — Version 4

Generates version 4 UUIDs in bulk from your browser’s cryptographic random source.

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Processing happens locally in your browser. What you paste or load is processed by this page and is not uploaded to a server. Nothing is stored unless you use a control that says it stores something, and you can clear anything this site has kept from the privacy page.

How to use this tool

  1. Set how many you need.
  2. Choose the letter case, and braces if you are pasting into a Windows tool that expects them.
  3. Select Generate, then copy or download the list.

What uuid generator does

A version 4 UUID is 122 random bits written in a fixed 36-character layout, with six bits reserved to record the version and variant. Random is the whole design: no coordination, no central allocator, no round trip to a database to reserve an identifier. Two independently generated values colliding is not something worth engineering against.

These come from your browser’s cryptographic random source rather than from Math.random, which matters if an identifier is ever used somewhere a guessable value would be a problem. Worth knowing before you use one as a primary key: a random UUID has no order, so rows arrive scattered across the index rather than at the end of it, and on a large table that is a real cost. If you need both uniqueness and locality, look at the time-ordered UUID versions or a sortable identifier instead.

Frequently asked questions

They come from your browser’s cryptographic random source rather than Math.random. A version 4 UUID has 122 random bits, which is enough that a collision between independently generated values is not something worth designing around.

It is a real trade-off. A random UUID scatters inserts across the index instead of appending at the end, which costs page splits and cache misses on a large table, and it is four times the width of a 32-bit integer in every foreign key. If you want uniqueness without coordination, consider a time-ordered UUID version or a sortable identifier instead.

Nothing meaningful — GUID is Microsoft’s name for the same 128-bit value. The only visible difference is that Microsoft tooling often writes them in braces and in upper case, and both of those are options on this page.