UUID Generator

What a UUID is

A UUID (universally unique identifier), called a GUID in Microsoft tools, is a 128-bit value written as 32 hexadecimal digits in five groups, such as 3f2b8c1e-9d4a-4f6b-8e2a-1c7d5b9e0a13. UUIDs let different systems create identifiers independently without a central counter, which is why they are used for database keys, API request IDs, file names and distributed systems.

Version 4 UUIDs

This tool creates version 4 UUIDs, which are random: 122 of the 128 bits come from your browser's cryptographically secure random generator (crypto.randomUUID), and the remaining bits mark the version and variant. The chance of two random v4 UUIDs colliding is so small that you would need to generate billions per second for many years to expect one.

Formats

• Lowercase with hyphens is the standard form from RFC 9562 and what most databases and languages expect.
• Uppercase is common in Windows and .NET code.
• Without hyphens gives a compact 32-character string for URLs or file names.

When to use something else

If you need IDs that sort by creation time, consider UUID version 7 in your application code. For secrets such as API keys, a random password is more suitable: try the password generator. To create test data, pair UUIDs with the JSON formatter.

Using UUIDs in databases

Most databases have a native UUID type, such as uuid in PostgreSQL or UNIQUEIDENTIFIER in SQL Server, which stores the value in 16 bytes instead of a 36-character string. Random v4 keys spread inserts across the index, which can slow very large tables; time-ordered versions help there. UUIDs also make it safe to merge data from several sources and to create records on a device while offline, because each one is unique without asking a central server for the next number.

Because the values are random and unpredictable, UUIDs are also safer than counting numbers in public URLs, where visitors could otherwise guess other records.