UUID Generator

How to use UUID Generator

1. Set Quantity between 1 and 50 (default is one). Tick Uppercase or leave it off for lowercase hex, and choose whether to Include hyphens in the classic 8-4-4-4-12 layout.
2. Click Generate for fresh UUID version 4 values, or Nil UUID for the all-zeros identifier used as an empty sentinel in many APIs.
3. Use Copy all to place every line on the clipboard, or Clear to wipe the output and the validate field.
4. Optionally paste any UUID into the validate box and hit Check to confirm it is well-formed hex and, where detectable, which version nibble it carries.

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What a UUID is for

A UUID (Universally Unique Identifier) is a 128-bit value written as thirty-two hexadecimal digits, usually grouped with hyphens. Developers use them as primary keys, message IDs, session tokens, file names, and idempotency keys: anywhere you need an identifier that is extremely unlikely to collide without a central counter. UUID version 4 fills almost every bit from a cryptographically strong random source, which is why this tool relies on crypto.getRandomValues in your browser rather than a weak Math.random fallback.

Typical jobs include minting IDs for a prototype API, seeding fixture data, labelling uploads before a server responds, or generating batch keys for load tests. When you need login secrets rather than opaque IDs, use the Password Generator instead; for plain numeric draws, try the Random Number Generator.

Formats, Nil UUID and validation

Most systems expect the hyphenated lowercase form (for example 550e8400-e29b-41d4-a716-446655440000). Some databases and compact protocols prefer thirty-two characters with no separators; others insist on uppercase. This page lets you switch those options before you copy so you do not have to reformat by hand. The Nil UUID (00000000-0000-0000-0000-000000000000) is the official “empty” value, useful in tests and optional fields, not as a secret.

The optional validator accepts hyphenated or compact hex (and strips a leading urn:uuid: if present). It reports whether the string is valid hex of the right length and, when the version nibble is in the usual 1-8 range, which version it appears to be. Version 4 is what Generate produces; other versions you paste may come from libraries that embed timestamps or namespace hashes.

Privacy and browser support

Everything runs in your tab. UUIDs are not uploaded, logged or stored on Catpool’s servers. Refresh the page and you start clean, aside from the single UUID generated automatically on first load so the output is never empty when you arrive. Modern desktop and mobile browsers that expose the Web Crypto random API are supported; if that API is missing, the status line explains the failure rather than silently using insecure randomness.

If you are shaping JSON payloads that carry these IDs, the JSON Formatter and Base64 Encode / Decode tools sit in the same browser-only toolkit.

FAQ

Is a UUID a password?

No. UUIDs are identifiers, not credentials. Do not treat a random UUID as a substitute for a strong password or API secret with proper entropy and storage rules.

Can two UUID v4 values collide?

In practice, for everyday application volumes, collisions are vanishingly rare. Version 4 still depends on a good entropy source, which is why this tool refuses to fall back to insecure generators.

Why is there no UUID version 7 button?

Version 7 is time-ordered and easy to get subtly wrong (clock skew, counter bits, layout). This page focuses on solid version 4 plus Nil so you get correct, predictable output every time.

Do you store the UUIDs I generate?

No. Generation and validation happen entirely on your device. Nothing is sent to Catpool.

What quantity should I use?

One is enough for a single form field. Raise quantity when you need a pasteable list for fixtures or scripts, up to fifty lines per click.

Related: Password Generator, Random Number Generator, JSON Formatter, Base64 Encode / Decode, Unix Timestamp Converter, Developer, Catpool home.