Free UUID Generator
Generate random UUID v4 identifiers for databases, APIs, and testing. Create one or many at once.
Generate UUID
Bulk Generate
What is a UUID?
A UUID (Universally Unique Identifier) is a 128-bit identifier used to uniquely identify resources across systems without coordination. Also known as GUIDs (Globally Unique Identifiers) in Microsoft ecosystems.
UUID v4 Format
UUID v4 uses random or pseudo-random numbers. The standard format is:
Where x is any hex digit and y is one of 8, 9, a, or b. The 4 indicates version 4.
Common Use Cases
- Database primary keys — avoid sequential IDs that leak information
- API identifiers — unique resource IDs across microservices
- Session tokens — unique session identifiers
- File names — prevent collisions in storage systems
- Asset tracking — unique labels for physical items via QR codes
- Correlation IDs — trace requests across distributed systems
Frequently Asked Questions
What is a UUID v4, and how random is it?
A version 4 UUID is 128 bits, of which 6 are fixed to record the version and variant, leaving 122 random bits. That is roughly 5.3 undecillion possible values. The randomness is what makes them useful: two systems that have never communicated can each mint identifiers and safely assume they will not collide.
Are UUIDs guaranteed to be unique?
Not guaranteed — statistically assured, which in practice is stronger than it sounds. To reach a one-in-a-billion chance of a single collision you would need to generate around 103 trillion version 4 UUIDs. The real risk is never the mathematics; it is a weak random source. Generate them with a cryptographic random number generator, which is what this page and every modern platform use.
What is the difference between a UUID and a GUID?
Almost nothing. GUID is Microsoft's name for the same 128-bit identifier defined by RFC 9562, and the two terms are used interchangeably. The one thing to watch is that some Microsoft tooling prints a GUID inside braces and historically stored parts of it in little-endian byte order, so a byte-level comparison between platforms can differ even when the identifier is the same.
Should I use a UUID as a database primary key?
It depends on the version. Random v4 UUIDs scatter inserts across a B-tree index, which fragments pages and hurts write throughput on large tables. Version 7, added in RFC 9562, puts a millisecond timestamp in the high bits so values sort in creation order and insert sequentially, which removes most of that cost while keeping the decentralised generation. For a new schema that wants UUID keys, v7 is usually the better choice.
Can someone guess or predict a v4 UUID?
Not one generated from a cryptographic source — 122 random bits are far beyond brute force. But a UUID is an identifier, not a secret, and treating it as one is a common mistake. If a resource is protected only by an unguessable URL, then anything that leaks the URL — a referrer header, a shared link, a browser history, a proxy log — leaks the resource. Authorise the request as well.
Do UUIDs leak any information?
Version 4 does not; it is random throughout. Version 1 does, because it embeds a timestamp and, in the original scheme, the generating machine's MAC address. Version 7 embeds a timestamp by design, so a v7 identifier reveals roughly when the record was created. That is usually harmless and occasionally is not.
Does case or formatting matter when comparing UUIDs?
Hexadecimal digits are case-insensitive, so the same UUID may arrive uppercase from one system and lowercase from another. RFC 9562 says to output lowercase and accept either. Normalise before comparing, and strip any surrounding braces or urn:uuid: prefix, or two identical identifiers will fail a string comparison.
Are the UUIDs on this page generated in my browser?
Yes, using the browser's cryptographic random number generator. Nothing is requested from a server and nothing is stored or logged, so no identifier you generate here has ever existed anywhere else. A generator that mints identifiers on someone else's machine is worth avoiding on principle.
Encode UUIDs in QR Codes
The Scan & Generate app lets you create QR codes from UUIDs and scan them back — perfect for asset tracking and inventory.