UUID Generator

What this tool does

It mints UUIDs in your browser using crypto.getRandomValues(), the same cryptographically secure source your browser uses for TLS key material. Pick version 4 for pure randomness, version 7 when you want identifiers that sort by creation time, or the nil UUID when you need a well-known placeholder. Ask for one or ask for a thousand.

The formatting switches cover the shapes different ecosystems expect: bare lowercase for PostgreSQL and JSON, uppercase inside braces for the Windows registry and COM, the 32-character compact form for URLs, and the urn:uuid: prefix defined in RFC 9562 §4.

Common uses

• Seeding a database column or a fixture file with realistic primary keys.
• Creating a correlation ID to thread one request through several services' logs.
• Naming uploaded objects in S3 so two users cannot overwrite each other's file.
• Producing an idempotency key for a payment API that requires one per attempt.
• Filling a uuid field by hand while testing an endpoint in Postman or curl.

A short example

One value, shown in each supported format:

0190f6c2-4a51-7b19-8c3d-5e9a1b2c3d4e
0190F6C2-4A51-7B19-8C3D-5E9A1B2C3D4E
0190f6c24a517b198c3d5e9a1b2c3d4e
{0190f6c2-4a51-7b19-8c3d-5e9a1b2c3d4e}
urn:uuid:0190f6c2-4a51-7b19-8c3d-5e9a1b2c3d4e

Why version 7 is usually the better database key

A v4 UUID is 122 random bits with four pinned to the version and two to the variant. Two values created a second apart have no relationship, so inserting them into a B-tree index writes to a random leaf page every time. The index stops fitting in cache, pages split constantly, and a table that was fast at a million rows is noticeably slower at fifty million — the fragmentation problem that made people reach for auto-increment integers.

Version 7 fixes the ordering without giving up global uniqueness. Its first 48 bits are the Unix timestamp in milliseconds, big-endian, followed by the version nibble and 74 random bits. Sorting v7 values as text or as bytes puts them in creation order, so inserts land at the right-hand edge of the index the way a sequence would, and ORDER BY id becomes a usable proxy for ORDER BY created_at.

The trade is that a v7 value leaks when it was created, to the millisecond. If an identifier is exposed publicly and that timing is sensitive — sign-up order, say — use v4 there.

Worth knowing

Uniqueness is probabilistic, not guaranteed. With 122 random bits you would need to generate about 2.7 × 10¹⁸ v4 UUIDs before reaching a 50% chance of a single collision, which is why nobody checks. What does break uniqueness is a weak random source: UUIDs built on Math.random(), a bad server-side seed, or a container image that boots with the same entropy pool have all caused real duplicate-key incidents. This tool never calls Math.random().