Question 1

What is the difference between UUID v4 and UUID v7?

Accepted Answer

UUID v4 is fully random — 122 bits of randomness. UUID v7 is time-ordered: the first 48 bits are a Unix timestamp in milliseconds, followed by 74 bits of randomness. v7 is sortable by creation time, which makes it better for database primary keys.

Question 2

When should I use ULID instead of UUID?

Accepted Answer

Use ULID when you need lexicographic sortability, a shorter URL-safe representation (26 characters vs UUID’s 36), and Crockford Base32 encoding. ULID is essentially UUID v7 with a different encoding — both are time-ordered and 128 bits.

Question 3

When should I use NanoID instead of UUID?

Accepted Answer

Use NanoID when you want a shorter, URL-safe ID with a customizable alphabet and length. The default 21-character NanoID has a similar collision probability to UUID but is more compact. It is not time-ordered.

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