🆔 UUID Generator

What is the UUID Generator?

A UUID (Universally Unique Identifier), known in the Microsoft world as a GUID (Globally Unique Identifier), is a 128-bit value written as 32 hexadecimal digits in five groups separated by hyphens, for example 3f2504e0-4f89-41d3-9a0c-0305e82c3301. The format is fixed at 8-4-4-4-12 digits, so a UUID is always 36 characters long including the four hyphens. The point of a UUID is to let many different systems generate identifiers independently and still be confident the values will not collide, without any central authority handing out numbers.

There are several UUID versions. This tool produces version 4 UUIDs, which are built almost entirely from random data. Of the 128 bits, 6 are reserved to mark the version and the variant, leaving 122 bits that are random. That is why a v4 UUID is the safest choice for general use: it carries no timestamp, MAC address, or other identifying information, so it does not leak anything about the machine or moment that created it. You can spot a v4 UUID because the first digit of the third group is always 4, and the first digit of the fourth group is always 8, 9, a, or b.

The randomness here comes from the browser crypto API, specifically crypto.randomUUID() where available, with a crypto.getRandomValues() fallback that sets the version and variant bits by hand. Both draw from a cryptographically secure pseudo-random number generator, not the ordinary Math.random(). With 122 random bits the pool of possible values is so vast (around 5.3 undecillion) that you would need to generate billions of UUIDs per second for many years before a duplicate became remotely likely, which is why v4 UUIDs are treated as practically unique in real systems.

When to use it

• Creating primary keys for database rows when you want IDs that can be generated by the application rather than the database.
• Assigning unique identifiers to API requests, log entries, or distributed events so they can be traced across services.
• Naming files, test fixtures, or temporary resources where you need a value that will not clash with anything else.
• Generating correlation IDs, session tokens, or idempotency keys during local development and testing.

How to use the UUID Generator

1. Set how many UUIDs you want using the count field, anything from 1 to 50.
2. Optionally tick Uppercase or Wrap in braces to match the format your code or platform expects.
3. Press Generate to produce the batch (or change a setting, which regenerates automatically).
4. Click Copy next to a single UUID, or Copy all to copy the whole list at once.

Formula & method

Worked examples

Common UUID versions and how they are generated

Anatomy of a version 4 UUID

Common mistakes to avoid

• Assuming UUIDs are guaranteed unique. Version 4 UUIDs are random, so a collision is astronomically unlikely but not mathematically impossible. For critical systems still keep a unique constraint in the database rather than relying on the format alone.
• Using Math.random() to make UUIDs in code. Math.random() is not cryptographically secure and can repeat patterns. Use crypto.randomUUID() or crypto.getRandomValues() instead, which is what this tool does.
• Treating a v4 UUID as sortable. A v4 UUID contains no timestamp, so sorting a list of them gives a random order. If you need chronological ordering, use v7 or store a separate created-at timestamp.
• Mismatching case or braces. Some platforms expect lowercase, some expect uppercase GUIDs wrapped in braces. A UUID is case-insensitive in value, but a strict string comparison will fail, so match the format your system expects.

Glossary

UUID

Universally Unique Identifier, a 128-bit value written as 32 hexadecimal digits in an 8-4-4-4-12 pattern.

GUID

Globally Unique Identifier, Microsoft's name for the same 128-bit identifier, often shown wrapped in braces.

Version 4

A UUID generated almost entirely from random data, with only the version and variant bits fixed.

Variant

Two or three bits that mark which UUID layout is in use. For standard UUIDs the fourth group starts with 8, 9, a, or b.

CSPRNG

Cryptographically secure pseudo-random number generator, the kind of randomness the browser crypto API provides.

Frequently asked questions