RFC 9562 Universally Unique Identifier (UUID) Specifications
A Universally Unique Identifier (UUID) is a 128-bit label standardized under IETF RFC 9562 (superseding RFC 4122). Designed to enable distributed systems to generate unique primary keys without central coordination, UUIDs guarantee uniqueness across databases, session cookies, and API request headers.
UUID Version 4 vs. Version 7 Comparison
- UUID Version 4 (Pure Randomness): Generated using 122 bits of pseudo-random entropy. The collision probability is astronomically small (1 in 2^122), but random distribution causes severe B-Tree database index fragmentation.
- UUID Version 7 (Time-Ordered): Combines a 48-bit Unix epoch millisecond timestamp with 74 bits of random entropy. Because IDs are monotonically increasing over time, they index cleanly in PostgreSQL, MySQL, and SQLite without database page splits.
Standard Hexadecimal String Representation
UUIDs are formatted as 32 hexadecimal digits separated by four hyphens into five groups: 8-4-4-4-12 (e.g. f47ac10b-58cc-4372-a567-0e02b2c3d479).
Developer & Database Suite
Combine UUID generation with our webmaster utilities:
- Cryptographic Hashes: Compute SHA-256 digests with our Cryptographic Hash Generator.
- JSON Formatting: Structure API request payloads with our JSON Formatter & Validator.
- Base64 Encoding: Convert binary data with our Base64 Encoder / Decoder.
Frequently Asked Questions
What is the difference between a UUID and a GUID?
UUID (Universally Unique Identifier) is the open IETF standard name. GUID (Globally Unique Identifier) is Microsoft's terminology for the exact same 128-bit specification.
Why is UUID v7 recommended for database primary keys?
Because UUID v7 begins with a chronological timestamp, new records are appended sequentially to the end of database B-Tree index pages, improving database insert performance by up to 400% compared to random UUID v4.