OneStopWebTools

UUID Generator

Create universally unique identifiers for databases, APIs and test data. Generate up to 1,000 at once as random version 4 UUIDs or time-ordered version 7 UUIDs, format them the way your system expects, and inspect any UUID to find its version and, where present, its creation time.




  
Inspect a UUID

  

  



  


  

  

    
    

      
Step-by-step guide: UUID v4 vs v7: Which Should You Use?

      
How to use the UUID Generator


  1. Choose version 4 for general-purpose random IDs, or version 7 when IDs will be used as database keys and should sort by creation time.
  2. Enter how many you need (up to 1,000) and pick a format.
  3. Select Generate UUIDs, then copy them or download a text file with one per line.
  4. To check an existing ID, paste it into Inspect a UUID to see whether it is valid, its version and variant, and the timestamp encoded in version 1, 6 and 7 UUIDs.

      
Example: v4 and v7 side by side


v4  3f2b8c1e-9a4d-4f7b-8e21-6c0d5a9b7e14
v7  019a2c4e-7b31-7c8d-9f02-4e6a1b3c5d70


In both, the first digit of the third group shows the version (4 or 7), and the first digit of the fourth group (8, 9, a or b) marks the standard RFC 9562 variant. In the v7 UUID, the first 12 hex digits encode the creation time in milliseconds, so v7 IDs created later sort after earlier ones.

      
What UUIDs are for


A UUID (also called a GUID) is a 128-bit identifier that can be generated independently on any machine with a negligible chance of ever colliding with another. That makes UUIDs ideal when records are created in many places — mobile apps, distributed services, offline clients — without asking a central server for the next ID.

      
Version 4 or version 7?


Version 4 UUIDs contain 122 random bits. Generating a billion per second for about 85 years would give roughly a 50% chance of a single duplicate. They reveal nothing about when or where they were made.


Version 7, standardised in RFC 9562 (2024), starts with a 48-bit Unix timestamp in milliseconds followed by 74 random bits. Because new IDs are always larger than older ones, they keep database indexes compact and insertion fast, while remaining unique. The trade-off is that anyone who sees a v7 UUID can tell roughly when it was created.

      
How they are generated here


Random bits come from crypto.getRandomValues(), your browser’s cryptographically secure random number generator — not Math.random(), which is predictable. The version and variant bits are then set as RFC 9562 requires. For version 7, IDs generated in the same millisecond have their random portion incremented, so a batch stays strictly in order.

      
Limitations to keep in mind


  • Up to 1,000 UUIDs per batch.
  • Version 1, 3, 5 and 6 UUIDs are not generated, though they can be inspected.
  • Version 7 timestamps come from your device clock; if it is wrong, the encoded time will be too.

      
How your data is handled


UUIDs are generated in your browser and are not logged or stored anywhere, so no one else has a record of the IDs you create.

      

        
Frequently asked questions

        
Are UUIDs really unique?
Not mathematically guaranteed, but the probability of a collision with properly generated random UUIDs is so small that it can be ignored in practice.
What is the difference between a UUID and a GUID?
They are the same thing. GUID (globally unique identifier) is the name Microsoft uses; the format is identical.
Should I use UUIDs as database primary keys?
They work well, especially version 7, which inserts in order like an auto-incrementing number. Random v4 keys can fragment indexes in large tables.
Can I use a UUID as a secret token?
A v4 UUID has 122 random bits, which is hard to guess, but tokens should normally come from a purpose-built generator in your framework. v7 UUIDs are partly predictable and should never be used as secrets.