UUID Generator

What is a UUID?

A UUID (Universally Unique Identifier) is a 128-bit value, usually written as 32 hexadecimal characters in five hyphen-separated groups, designed so that two randomly generated UUIDs are astronomically unlikely to ever collide — no coordination between systems needed. This tool generates version 4 UUIDs, the fully-random variant, using crypto.randomUUID(), your browser's built-in cryptographically secure random number source.

Common uses

• Database primary keys and record IDs
• Unique request or trace IDs for logging and debugging
• Generating test data or placeholder identifiers

How a version 4 UUID is laid out

A UUID is written as 8-4-4-4-12 hexadecimal characters, for example 3f2b8c1e-9a4d-4e7b-b6a1-0c5d2f8e7a91. Of its 128 bits, 6 are fixed: the first character of the third group is always 4 (the version), and the first character of the fourth group is always 8, 9, a or b. That leaves 122 random bits, or about 5.3 × 10^36 possible values.

How unlikely is a collision?

Generating a billion UUIDs every second, you would need to run for roughly 86 years to reach a 50% chance of a single duplicate. For ordinary applications, from a few thousand to a few billion records, the risk is negligible, and it is usually far lower than the risk of a bug somewhere else in the system.

Practical notes

• You can generate 1 to 100 at once. The Uppercase option only changes how they are displayed; the value is the same.
• Fully random keys are inserted in random order, which can slow indexes on very large database tables. Time-ordered formats such as UUID version 7 (defined in RFC 9562) are designed for that case.
• A UUID is an identifier, not a secret. Don't use one as a password or as the only protection for a private link.
• Most databases and languages accept the hyphenated lowercase or uppercase form, but check whether yours expects braces or no hyphens.

Using the generated values

You can ask for between 1 and 100 UUIDs at a time, and changing the count creates a fresh set. Each one is 36 characters long: 32 hexadecimal digits and 4 hyphens. Copy All joins them with line breaks, so a full set of 100 comes to 3,699 characters (100 × 36 plus 99 breaks), ready to paste into a spreadsheet column or a seed script. The Uppercase option only changes how the letters are shown and copied, so 3f2b8c1e-9a4d-4e7b-b6a1-0c5d2f8e7a91 becomes 3F2B8C1E-9A4D-4E7B-B6A1-0C5D2F8E7A91, which most systems treat as the same value.

If a system stores UUIDs as text, remember that a hyphenated one takes 36 bytes, or 32 without the hyphens, while the same value as binary takes 16 bytes, which is why databases with a native UUID type are more compact. Random version 4 values have no order, so using them as the primary key of a very large table scatters new rows across the index; time-ordered identifiers are a better fit when insert speed matters. The generator needs a page served over HTTPS, since browsers only offer the random UUID function in a secure context.