GUID vs UUID
GUID (Globally Unique Identifier) and UUID (Universally Unique Identifier) refer to the same 128-bit identifier. They are functionally identical; the difference is only in naming and ecosystem.
Key differences
| UUID | GUID | |
|---|---|---|
| Standard | RFC 4122 / RFC 9562 | Microsoft (uses RFC 4122) |
| Common in | Web, Linux, RFCs, databases | Windows, .NET, COM |
| String form | lowercase, hyphenated | often wrapped in curly braces |
| Byte order | big-endian (network order) | mixed-endian in .NET Guid struct |
The byte-order gotcha
In string form they are identical. But the .NET Guid struct stores the first three fields as little-endian, so Guid.ToByteArray() returns a different byte sequence than the canonical UUID representation. When interoperating, compare by string, not by raw bytes.
Which should you use?
Use the term UUID for cross-platform and standards-based work. Use GUID within the Microsoft ecosystem. The generated values are interchangeable at the string level.
Try our Converter to switch between hyphenated, hex, uppercase and GUID brace forms.