A UUID validator checks whether a string follows the universally unique identifier format and reports which version and variant it is. Paste a UUID into the tool below and it tells you, entirely in your browser, whether the value matches the 8-4-4-4-12 hexadecimal pattern and what its version digit means.
What a UUID Is and Its 8-4-4-4-12 Format
A UUID, or universally unique identifier, is a 128-bit value used to label something without a central authority handing out numbers. It is written as 32 hexadecimal digits split into five groups by hyphens, in the pattern 8-4-4-4-12, such as 123e4567-e89b-12d3-a456-426614174000. Because the space of possible values is so large, two systems can each generate a UUID and the chance of a collision stays negligible. The validator’s first job is to confirm a string matches that exact pattern, since anything outside it is not a UUID.
How to Use It
- Paste the value you want to check into the input box.
- The tool checks it as you type and reports PASS or FAIL.
- On a PASS, read the version digit to learn how the UUID was created.
- Read the variant to confirm it follows the RFC 4122 layout that most software expects.
- An all-zero value is reported as the nil UUID, the placeholder that means no value.
The UUID Versions and How to Tell Them Apart
The version is the first digit of the third group. It tells you the method used to build the identifier, which matters when you need to know whether a value is random, time based, or derived from a name.
| Version | How it is made | How to tell |
|---|---|---|
| v1 | Timestamp plus the machine’s MAC address | Third group starts with 1 |
| v3 | A name hashed with MD5 | Third group starts with 3 |
| v4 | Random values | Third group starts with 4 |
| v5 | A name hashed with SHA-1 | Third group starts with 5 |
When to Use It
Reach for the validator when a database insert rejects an identifier, when an API returns an error about a malformed id, or when you copy a UUID from a log and want to confirm it was not truncated. It also helps when you need to know which version you are dealing with, for example confirming a value is a random v4 before you rely on it being unpredictable, or spotting a v1 that carries a timestamp and machine address you may not want to expose.
Last Thoughts on Validating UUIDs
Checking a UUID by eye is error prone, because a missing digit or an extra hyphen is easy to miss in a long hexadecimal string. The validator removes the guesswork: it confirms the 8-4-4-4-12 shape, then reads the version and variant from their fixed positions so you know not just that the value is well formed but how it was created.
If you need to create one, use our UUID generator. For other format checks, see the Luhn validator and the regex tester, and browse the rest of our free online tools.
Key Takeaways:
- A valid UUID is 32 hexadecimal digits in five hyphen-separated groups following the 8-4-4-4-12 pattern.
- The version is the first digit of the third group; v4 means random, v1 means time based, v3 and v5 are name based.
- The variant is the first digit of the fourth group; 8, 9, a, or b marks the standard RFC 4122 layout.
- The all-zero nil UUID is valid and is used as a placeholder that means no value.
- The validator runs in your browser, so the value you paste is never sent anywhere.
Frequently Asked Questions (FAQs)
What makes a UUID valid?
A valid UUID is 32 hexadecimal digits arranged in five groups separated by hyphens, in the pattern 8-4-4-4-12. Only the characters 0 through 9 and a through f are allowed. Any other length, character, or spacing means the string is not a UUID.
How do I find the version of a UUID?
Read the first digit of the third group. That single character is the version: 1 for time based, 3 for an MD5 name hash, 4 for random, and 5 for a SHA-1 name hash. The validator reads it for you and explains what it means.
What is the variant in a UUID?
The variant is the first digit of the fourth group and tells you which layout standard the UUID follows. When that digit is 8, 9, a, or b, the UUID uses the common RFC 4122 layout that most software expects.
Is the nil UUID valid?
Yes. The nil UUID is all zeros, written as 00000000-0000-0000-0000-000000000000. It is a valid value used as a placeholder to mean no value or none, and the validator reports it as such rather than as an error.
Are UUIDs case sensitive?
No. The hexadecimal letters can be uppercase or lowercase and the UUID means the same thing either way. The validator accepts both, though many systems store and display UUIDs in lowercase by convention.
Does this tool send my UUID to a server?
No. The check runs entirely inside your browser using a pattern match, and the value you paste is never transmitted, logged, or stored. You can confirm this by disconnecting from the internet and watching it still work.
