UUID Guide: Versions, Formats, and When to Use Each

A UUID (Universally Unique Identifier) is a 128-bit identifier that is practically guaranteed to be unique across time and space. UUIDs look like 550e8400-e29b-41d4-a716-446655440000—five groups of hexadecimal digits separated by hyphens.

UUID Versions

Version	Based On	Best For
v1	Timestamp + MAC address	Time-ordered IDs (leaks MAC)
v4	Random	Most common—general purpose IDs
v5	SHA-1 of namespace + name	Deterministic IDs from known inputs
v7	Unix timestamp + random	Sortable, database-friendly

UUID vs Auto-Increment

• Security: UUIDs don't reveal record count or creation order. Auto-increment IDs like /users/42 let attackers enumerate records.
• Distributed systems: UUIDs can be generated on any node without coordination. Auto-increment requires a central sequence.
• Merging databases: UUIDs don't collide when merging data from multiple sources.
• Downside: UUIDs are larger (16 bytes vs 4-8 for integers) and less readable.

Generating UUIDs

JavaScript:

crypto.randomUUID();
// "a3bb189e-8bf9-4888-9912-ace4e6543002"

Python:

import uuid
str(uuid.uuid4())
# "c9bf9e57-1685-4c89-bafb-ff5af830be8a"

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