GUID and UUID are the same thing — but v1, v4, and v7 are very different. Here's how to pick.
If you've ever generated an ID and wondered whether you needed a "UUID" or a "GUID", here's the short answer: they're the same thing. The longer, more useful answer is that the version you pick (v1, v4, or the newer v7) matters a lot more than the name. Let's clear both up.
Need one right now? Our GUID / UUID generator produces valid identifiers instantly.
A UUID (Universally Unique Identifier) is a 128-bit value defined by RFC 4122, usually written as 32 hex digits in five dash-separated groups: 550e8400-e29b-41d4-a716-446655440000. GUID (Globally Unique Identifier) is Microsoft's name for the exact same thing. If you're in the .NET/Windows world you'll hear "GUID"; everywhere else it's "UUID". Same 128 bits, same format, interchangeable.
The 13th hex digit encodes the version. The common ones:
122 random bits. This is what most generators produce and what you almost always want: no coordination, no central authority, effectively zero collision risk. The downside is that random UUIDs are unordered, which matters for databases (more below).
Encodes the current time and the machine's network card address. It's time-ordered, but it leaks the MAC address and creation time, which is a privacy and security concern. Rarely the right choice today.
Ratified more recently, v7 puts a Unix millisecond timestamp in the high bits and random data in the rest. You get the collision-resistance of v4 plus natural sort order — without leaking a MAC address. For new systems that store IDs in a database, v7 is increasingly the best default.
Databases store rows in index order. When you insert random v4 UUIDs as a primary key, every insert lands in a random spot in the B-tree, fragmenting the index and hurting write performance and cache locality. Time-ordered IDs (v7, or ULIDs) insert at the "end" of the index, which is far friendlier. If you're choosing a primary-key strategy: v4 for opacity, v7 for database-backed primary keys.
User-facing short links or codes — 36 characters is ugly in a URL. Use a shorter scheme.
Anything needing guaranteed monotonic ordering — a database sequence is simpler.
Cryptographic secrets — a v4 UUID has 122 bits of randomness, which is strong, but use a purpose-built token generator for auth secrets so intent is explicit. Our password generator is a better fit there.
Just need a unique ID with no fuss → v4.
Database primary key, want sortable inserts → v7.
Interop with a legacy system that asks for v1 → v1, but understand the trade-off.
Whichever you need, generate a valid, correctly-versioned identifier with the GUID / UUID generator — no signup, runs in your browser.
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