UUID Generator
100% private — runs on your device, never uploaded. Works offline once loaded.
Generate cryptographically random version-4 UUIDs (also called GUIDs) — one or several at a time. Everything is generated locally in your browser.
What a UUID actually contains
A UUID (Universally Unique Identifier) is a 128-bit value, almost always written as 32 hex digits split into five groups like f47ac10b-58cc-4372-a567-0e02b2c3d479. The version this tool produces, v4, sets aside a handful of fixed bits to mark it as version 4 and fills the remaining 122 bits with cryptographically random data. That's a big enough space that generating a billion UUIDs per second for a hundred years wouldn't approach a meaningful chance of a collision — which is exactly why databases, distributed systems and APIs use them instead of counters.
Why not just use auto-increment IDs
A simple incrementing integer (1, 2, 3…) works fine for a single database table, but breaks down the moment you have multiple servers, offline clients, or merging datasets — two systems generating IDs independently will collide. UUIDs solve this without any coordination between systems: any client, anywhere, can mint an ID that's guaranteed (for practical purposes) not to clash with one generated somewhere else. That's why they show up in distributed databases, mobile apps that create records offline, event-tracking systems, and as primary keys in microservice architectures.
- Distributed systems where no central authority assigns IDs
- Session tokens, request-trace IDs, and idempotency keys in APIs
- Test fixtures and seed data where you need guaranteed-unique placeholder values
v4 versus other UUID versions
Not all UUIDs are random. Version 1 embeds a timestamp and the generating machine's network address, which leaks information and is largely avoided today. Version 5 is deterministic — it hashes a namespace and a name so the same input always produces the same UUID, useful for de-duplication. Version 7, a newer addition to the spec, is time-ordered so UUIDs sort chronologically, which helps database index performance. When people say "just give me a UUID" with no other requirement, v4 — pure randomness — is almost always what they mean, which is why it's the default everywhere from uuidgen to language standard libraries.
Formatting details that trip people up
UUIDs are technically case-insensitive, but conventions differ: some systems expect lowercase hex, others uppercase, and some strip the hyphens entirely for use as a compact string key. If you're pasting a batch of generated UUIDs into a SQL insert statement, a JSON test fixture, or an environment file, generate more than you think you'll need — it's far cheaper to have a few spares than to break your flow regenerating one at a time.
Frequently asked questions
What is a UUID v4?
A version-4 UUID is a 128-bit identifier made from random data, used to uniquely identify records without a central authority.
Are they truly random?
Yes — they use your browser's cryptographically secure random generator.
Are they truly random, and could two ever collide?
They're generated using your browser's cryptographically secure random source, and with 122 random bits the odds of a collision are astronomically small — not zero in theory, but not a practical concern even at massive scale.
Is a UUID the same thing as a GUID?
Yes for practical purposes — GUID is Microsoft's term for the same 128-bit identifier format defined by the UUID standard, and the two are interchangeable in almost every context.
Can I use a UUID as a database primary key?
Yes, and it's common in distributed systems, though be aware random UUIDs can fragment index performance more than sequential IDs on very large, high-write tables — version 7 (time-ordered) UUIDs address that if it matters for your case.
Does uppercase versus lowercase matter?
UUIDs are case-insensitive by spec, but some systems expect one convention consistently — check what your database or API expects before mixing cases in the same dataset.
How many UUIDs can I generate at once here?
You can generate a batch in one go for seeding test data or fixtures; if you need an extremely large batch for a production import, generating in a script may be more practical than pasting from a browser tool.
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