Are UUID v4 values guaranteed unique?

Not guaranteed, but the collision probability is astronomically small — v4 uses 122 random bits, so you would need to generate billions before a collision becomes remotely likely.

What is the difference between UUID and ULID?

UUID v4 is fully random. ULID is also 128-bit but is time-sortable (its leading bits encode a timestamp) and uses a more compact, URL-friendly encoding.

Answer

How to generate a UUID (v4)

Generate random UUID v4 identifiers instantly in your browser. Free, private, generate one or many.

A version-4 UUID is a 128-bit random identifier written as 36 characters in the form 8-4-4-4-12 hex digits, e.g. f47ac10b-58cc-4372-a567-0e02b2c3d479. Open a UUID generator and it produces one (or many) using your browser’s cryptographically secure random source.

Input

(click Generate)

Output

f47ac10b-58cc-4372-a567-0e02b2c3d479

The 13th hex digit is always 4 (the version); the 17th is 8, 9, a, or b (the variant).

Open the UUID Generator → Free · runs in your browser · nothing uploaded

Steps

Open the UUID tool — a fresh v4 UUID is generated immediately.
Click Generate again for a new one, or set a count to produce many at once.
Copy a single UUID or copy the whole batch.
UUIDs are generated locally in your browser, so they never touch a server.

Frequently asked questions

Are UUID v4 values guaranteed unique?: Not guaranteed, but the collision probability is astronomically small — v4 uses 122 random bits, so you would need to generate billions before a collision becomes remotely likely.
What is the difference between UUID and ULID?: UUID v4 is fully random. ULID is also 128-bit but is time-sortable (its leading bits encode a timestamp) and uses a more compact, URL-friendly encoding.

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