UUID Generator
Generate RFC 4122 UUID v4 identifiers instantly in your browser. Generate one or a batch of UUIDs. Uses crypto.randomUUID() — no server, no tracking.
UUID Generator
Runs entirely in your browser — no server calls, no tracking.
Click Generate UUIDs to begin.
🔒 Your data never leaves this tab. This tool has no backend.
About the UUID Generator
A UUID (Universally Unique Identifier) is a 128-bit identifier standardised in RFC 4122 that is statistically guaranteed to be unique without any central coordination. UUID v4 uses cryptographically random bits — this tool calls crypto.randomUUID(), which uses the browser's cryptographically secure pseudo-random number generator (CSPRNG). The probability of generating a duplicate across all UUID v4 values ever created is astronomically small.
Where UUIDs are used
UUIDs are primary keys in databases where you cannot predict the next ID (distributed systems, multi-region writes, client-side insert before server confirmation). They are used as session tokens, request trace IDs, file upload identifiers, API key prefixes, and unique identifiers for objects in event logs. Because they are generated without a server call, clients can assign IDs locally and sync to the server later.
UUID v4 vs other versions
UUID v1 encodes the current timestamp and MAC address — identifies when and where it was created but leaks machine information. UUID v3 and v5 are name-based (deterministic hashes of a name + namespace) — use these when you need the same input to always produce the same UUID. UUID v4 is fully random — use it when uniqueness is the only requirement. UUID v7 (emerging) is time-ordered random, suitable for database primary keys because it produces sequential values that index efficiently.
UUID, GUID, and which version to generate
A UUID is a 128-bit identifier written as 36 characters — 32 hexadecimal digits in five hyphenated groups. GUID (Globally Unique Identifier) is Microsoft's name for exactly the same thing, so a UUID generator and a GUID generator are interchangeable.
| Version | Built from | Use it when |
|---|---|---|
| v4 | Random data | Default choice for almost everything |
| v7 | Timestamp + random | Database keys — sorts by creation time |
| v1 | Timestamp + MAC address | Legacy; leaks the generating machine |
| v5 | SHA-1 of a namespace + name | Same input must always give the same ID |
Will two v4 UUIDs ever collide?
In practice, no. A v4 UUID has 122 random bits, giving about 5.3 × 1036 possible values. You would need to generate roughly a billion per second for around 85 years before a single collision became likely. Application-level collision handling is not something you need to write.
UUIDs as database primary keys
The traditional objection is that random v4 values scatter inserts across a B-tree index, hurting write performance and cache locality on large tables. Version 7 fixes this by putting a timestamp in the high bits, so new IDs sort roughly in creation order while staying unique — you get the distributed-generation benefit without the index fragmentation.
Format variations
The canonical form is lower case with hyphens. Some systems want it upper case, some strip the hyphens to a 32-character string, and SQL Server wraps it in braces. These are all the same identifier in different clothing — compare them case-insensitively and normalise before storing.
Frequently asked questions
Nothing functional. GUID (Globally Unique Identifier) is Microsoft's name for the same 128-bit value that the rest of the world calls a UUID. Both are 36 characters — 32 hexadecimal digits in five hyphenated groups — and a generator for one produces valid output for the other.
Version 4 for almost everything: it is purely random with no information leakage. Use version 7 for database primary keys, since its timestamp prefix keeps inserts in roughly sequential order and avoids index fragmentation. Avoid version 1, which embeds the generating machine's MAC address.
Effectively never. A version 4 UUID has 122 random bits, or about 5.3 × 10^36 possible values. Generating a billion per second, you would wait roughly 85 years before a collision became likely. You do not need application-level collision handling.
Version 7 UUIDs are, and version 4 can be with care. The classic problem is that random v4 values scatter writes across the index, which slows inserts on large tables. Version 7 puts a timestamp in the high bits so new keys sort in creation order, keeping the benefits without the fragmentation.
Yes. They are produced in your browser using the built-in cryptographic random source, and nothing is sent to or stored on a server. The page works offline.
xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx. The "4" at position 13 indicates version 4. The "y" at position 17 is one of 8, 9, a, or b (indicating variant 2, which is RFC 4122). Total: 36 characters including hyphens.crypto.randomUUID(), the same browser API that production applications use client-side. The values are as cryptographically random as anything generated server-side with Node's crypto.randomUUID() or Python's uuid.uuid4().Need a distributed system or custom API built?
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