A UUID (Universally Unique Identifier) is a 128-bit number used to uniquely identify information in computer systems. Displayed as 32 hexadecimal digits in five groups separated by hyphens (e.g., 550e8400-e29b-41d4-a716-446655440000), UUIDs can be generated independently by any system with a near-zero probability of collision, eliminating the need for a central ID authority.
The most commonly used versions are UUID v4 (random) and UUID v7 (time-ordered random). UUID v4 generates 122 random bits, giving approximately 5.3 x 10^36 possible values -- enough that generating 1 billion UUIDs per second for 85 years would produce only a 50% chance of a single collision. UUID v7 embeds a Unix timestamp in the first 48 bits, making IDs naturally sortable by creation time while retaining enough randomness to avoid collisions.
UUIDs are used as primary keys in databases, session identifiers, API request IDs, distributed system correlation IDs, and anywhere a globally unique identifier is needed without coordinating with a central server.
In distributed systems, you cannot rely on a single database auto-incrementing an ID. Services running on different continents need to create identifiers independently and merge data later without conflicts. UUIDs solve this problem elegantly. They are also more secure than sequential IDs for public-facing resources, since an attacker cannot guess the next ID or enumerate all existing records.
TerminalFeed provides a UUID Generator tool that creates v4 and v7 UUIDs instantly in the browser, with bulk generation and format options. The TerminalFeed API uses UUIDs internally for request tracking and cache keys.