UUID (Universally Unique Identifier) is a 128-bit identifier standardized by RFC 9562. It is used to uniquely identify information in computer systems. A UUID is typically represented as 32 hexadecimal digits displayed in five groups separated by hyphens, like 550e8400-e29b-41d4-a716-446655440000.

What is the difference between UUID versions?

UUID v1 is time-based using timestamp and MAC address. UUID v4 uses random numbers for all bits. UUID v5 generates deterministic IDs from a namespace and name using SHA-1 hashing. UUID v4 is the most commonly used for general purpose unique ID generation due to its randomness.

Are UUIDs truly unique?

UUID v4 uses 122 random bits, giving approximately 5.3×10^36 possible values. The probability of collision is extremely low — practically zero for most applications. However, no random generation is theoretically guaranteed unique; the chance of collision increases with the number of UUIDs generated (birthday paradox).

Can I generate a UUID without hyphens?

Yes. Some tools and libraries support generating UUIDs without hyphens (also called 'clean UUIDs' or 'compact UUIDs'). These are 32-character hexadecimal strings that can be useful when UUIDs are used in contexts where hyphens are inconvenient, such as database keys or filenames.

A nil UUID is the special UUID value 00000000-0000-0000-0000-000000000000 where all 128 bits are zero. It is used as a sentinel value to indicate 'no UUID' or 'unknown UUID' in various systems and specifications.

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