Generate Random UUIDs Online

A UUID (universally unique identifier) is a 128-bit value that is practically unique without any central coordination. Version 4 UUIDs are random, which makes them popular as database keys and request IDs.

This tool generates v4 UUIDs in your browser using the Web Crypto API.

Key features

• Version 4 (random) UUIDs
• Generate up to 500 at a time
• Uppercase and no-hyphen options
• Cryptographically secure randomness

Example

3b241101-e2bb-4255-8caf-4136c566a962

How to use

1. Choose how many UUIDs you need.
2. Set the format options.
3. Click Generate and copy the list.

Use cases

• Seeding test data
• Creating unique IDs for records and requests
• Generating correlation IDs for logs

In depth

A UUID is a 128-bit identifier written as 32 hexadecimal digits in groups of 8-4-4-4-12, defined in RFC 4122 and updated by RFC 9562. In a version 4 UUID, 6 bits are fixed: four bits give the version, the digit 4 at the start of the third group, and two bits give the variant, which makes the first digit of the fourth group 8, 9, a or b. That leaves 122 random bits, or about 5.3 times ten to the power 36 possible values.

Collisions are therefore extremely unlikely: you would need to generate around 2.7 quintillion UUIDs to reach a 50 percent chance of one duplicate. That holds only when the random source is good, which is why the Web Crypto API matters; Math.random is not suitable. Pure random UUIDs do have a downside as database primary keys, since they scatter inserts across an index. Time-ordered versions such as v7 in RFC 9562 are designed to address that.

Tips

• Read the version digit if you need to confirm a UUID is v4. The first character of the third group should be 4, and anything else was made by a different method.
• Store UUIDs in a native uuid or binary 16 column where your database supports it. A 36 character text column uses more than double the space and makes indexes larger.
• Do not use a UUID as a password, session secret or access token on its own. It is meant to be unique, and any structure in it may make it more guessable than a purpose-built random token.

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