UUID v4 Generator

About UUID v4 Generator

Creates version 4 UUIDs, the 128-bit random identifiers written as 32 hexadecimal digits in an 8-4-4-4-12 pattern. Developers use them as database keys, request IDs, upload filenames and test fixtures whenever a unique value must be produced anywhere without asking a central counter.

How to use it

1. Type how many identifiers you need in Number of UUIDs. The page accepts 1 to 100, and one UUID is already generated when you arrive.
2. Switch on Uppercase if the system you are feeding expects capital A to F.
3. Switch off Include hyphens to get the compact 32-character form.
4. Select Generate UUIDs. Each press replaces the previous list.
5. Copy a single row with its icon button, or use Copy All to grab the whole list separated by line breaks.

Shape of every result (the digits themselves are random)

Number of UUIDs: 1, Uppercase off, Include hyphens on

xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx
Every x is a random hex digit. The 4 is fixed, and y is always one of 8, 9, a or b.

When to use it

• Generating primary keys for rows you insert from several services at once, with no coordination between them.
• Creating idempotency keys or correlation IDs to attach to API requests while debugging.
• Naming uploaded files so two users can never overwrite each other's document.
• Filling a spreadsheet or JSON fixture with unique ID values for a demo.

Questions about UUID v4 Generator

What do the fixed 4 and the 8, 9, a or b mean?

The first digit of the third group is the version number, 4 for random UUIDs. The first digit of the fourth group carries the variant bits, which is why it can only be 8, 9, a or b. That leaves 122 truly random bits.

Could two generated values ever collide?

With 122 random bits you would need to produce roughly 2.7 quintillion UUIDs before the chance of even one duplicate reaches 50 percent. For any realistic table or log, collisions are not a practical concern.

Where does the randomness come from?

The page asks the browser's cryptographic generator, crypto.getRandomValues, for its bytes. Only in an environment without that function does it fall back to Math.random, which is weaker.

Should I use one as a secret token?

A UUID is an identifier, and the standard does not promise it is unguessable. For passwords or API secrets, use a generator built for that job, where length and alphabet are under your control.

Is a random UUID a good database primary key?

It works, but fully random values scatter inserts across an index, which slows very large tables. Time-ordered UUID versions were designed for that case; this page produces version 4 only.

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