Question 1

What is a UUID?

Accepted Answer

A UUID (Universally Unique Identifier) is a 128-bit identifier standardized as RFC 4122. It's formatted as 32 hex digits split into 5 groups: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx. UUIDs are used as primary keys in databases, resource identifiers in APIs, session tokens, and anywhere a unique ID is needed without central coordination.

Question 2

What is the difference between UUID v1, v4, and v7?

Accepted Answer

UUID v1 encodes a timestamp and MAC address — sortable chronologically but reveals creation time and machine identity. UUID v4 is purely random — 122 bits of randomness with no information leakage. UUID v7 (RFC 9562) combines a Unix millisecond timestamp with random bits — it's both random and sortable, making it ideal for database primary keys.

Question 3

Is UUID v4 truly unique?

Accepted Answer

With 122 bits of randomness, the probability of collision is astronomically low. Generating 1 billion UUIDs per second for 100 years gives a collision probability of about 50% — meaning for any practical application, UUID v4 collisions are effectively impossible.

Question 4

Are UUIDs safe to use as public IDs?

Accepted Answer

UUID v4 is safe — it reveals no information. UUID v1 reveals your creation timestamp and MAC address (privacy concern). UUID v7 reveals only the creation timestamp. For public-facing IDs where creation time shouldn't be exposed, use UUID v4.

Question 5

Why use UUID v7 for database primary keys?

Accepted Answer

UUID v7's timestamp prefix makes it monotonically increasing (within the same millisecond, random), so B-tree index insertions are sequential rather than random. This dramatically reduces index fragmentation and improves write performance compared to random UUID v4 primary keys.

Question 6

How do I generate a UUID?

Accepted Answer

Click Generate above to create a new UUID v4 (random) using the browser's Web Crypto API. UUID v4 generates 122 random bits with a specific format: xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx where y is 8, 9, A, or B. UUIDs have an astronomically low collision probability making them safe for distributed ID generation without coordination. For GUID format (Windows), both are identical.

Question 7

What is the difference between UUID and GUID?

Accepted Answer

UUID (Universally Unique Identifier) and GUID (Globally Unique Identifier) are the same thing — GUID is Microsoft's term for UUID. Both follow RFC 4122 format: 32 hex digits in 5 groups separated by hyphens (xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx). UUID v4 is random; UUID v1 includes a timestamp and MAC address. Use DevDecode's GUID Generator if you need GUID-specific formatting.

UUID Generator — Free Online UUID v1 / v4 / v7 Generator

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