UUID Generator

What is a UUID?

A UUID (universally unique identifier), also called a GUID (globally unique identifier), is a 128-bit value used to label information in computer systems. It is written as 32 hexadecimal digits split by hyphens into five groups — 8-4-4-4-12 — for example 550e8400-e29b-41d4-a716-446655440000. Because UUIDs are unique in practice without any central coordination, they appear everywhere: database primary keys, API request IDs, file names, session tokens and distributed systems.

How to use this tool

1. Choose how many UUIDs you need — anywhere from 1 to 100.
2. Optionally switch on UPPERCASE or No hyphens to change the output format.
3. Click Generate (then Regenerate) for a fresh batch.
4. Use the Copy button next to any UUID, or Copy all to copy the whole list, one per line.

UUID versions: v1 vs v4

The UUID standard (RFC 4122) defines several versions. The two you will meet most often are:

• Version 1 (time-based): built from the current timestamp and the generating machine's MAC address. v1 UUIDs are roughly sortable by creation time, but they reveal when — and on which machine — they were made.
• Version 4 (random): 122 of the 128 bits are purely random, drawn here from your browser's cryptographically secure random generator. v4 is the most widely used version and the one this tool generates.

Everything runs locally in your browser: the UUIDs are created on your device and are never sent anywhere.

Common mistakes when working with UUIDs

• Truncating for short IDs. Keeping only the first 8 hex digits leaves 32 random bits, and the birthday bound puts a 50% collision chance near 77,000 IDs. Shortening a UUID recreates the exact problem UUIDs were designed to avoid.
• Building IDs with Math.random(). Copy-pasted snippets based on it are neither collision-safe nor unpredictable; use crypto.randomUUID(), as this tool does.
• Storing UUIDs as text. The hyphenated string costs 36 bytes per value. In MySQL, UUID_TO_BIN() converts to 16 bytes, and PostgreSQL has a native 16-byte uuid type. Smaller keys mean smaller indexes and faster joins.
• Mixing formats in comparisons. An uppercase, hyphenless value will not string-match its lowercase hyphenated twin. Normalize to one format everywhere, or compare the binary value.

Pro tips

• Toggling UPPERCASE or No hyphens re-formats the current batch in place; the IDs are kept, so you never need to regenerate and lose them.
• Copy all joins the batch one UUID per line: paste straight into a spreadsheet column, a SQL IN list, or a fixtures file.
• Counts above 100 are clamped to 100; for larger batches, generate, copy, and repeat.

Frequently asked questions