Question 1

What is a UUID?

Accepted Answer

128-bit unique identifier that looks like 550e8400-e29b-41d4-a716-446655440000. Use them for database IDs, session tokens, resource identifiers. Practically guaranteed to be unique without coordination.

Question 2

Which UUID version should I use?

Accepted Answer

v4 for general use (random). v7 for database primary keys (sortable by time, better performance). v5 when you need the same UUID from the same input (deterministic). Most people want v4 or v7.

Question 3

What's the difference between v4 and v7?

Accepted Answer

v4 is completely random. v7 includes a timestamp so it sorts chronologically. v7 is better for database primary keys because sorted IDs = better index performance. v4 is better when you don't want timestamps leaking creation time.

Question 4

Can two UUIDs ever be the same?

Accepted Answer

Technically possible, practically impossible. You'd need to generate billions per second for thousands of years to maybe get a collision. v4 has 122 random bits. That's 5.3×10³⁶ possible values.

Question 5

How do I use UUIDs as database primary keys?

Accepted Answer

Use v7 for new projects. Store as native UUID type (PostgreSQL: UUID, MySQL: BINARY(16)), not VARCHAR. Saves space: 16 bytes vs 36. Always index the column. v7's sortability reduces index fragmentation.

Question 6

What's the difference between UUID and GUID?

Accepted Answer

Same thing. UUID is the standard term. GUID is what Microsoft calls it. Both follow RFC-4122. Format is identical.

Question 7

Are UUIDs sortable?

Accepted Answer

v7, v6, v1: Yes, they have timestamps. v4, v5, v3: Nope, random or hash-based. Use v7 for database PKs if you want sorting.

Question 8

How do I generate deterministic UUIDs?

Accepted Answer

Use v5 (name-based). Same namespace + same name = same UUID every time. Pick a namespace (DNS, URL, etc), provide a string, get a UUID. Useful for generating IDs from URLs or emails without storing a mapping.

Question 9

What are the UUID output formats?

Accepted Answer

Standard: 550e8400-e29b-41d4-a716-446655440000. Uppercase: same but CAPS. No hyphens: 550e8400e29b41d4a716446655440000. URN: urn:uuid:.... GUID: {550e8400...} with braces. Base64: compact, 22 chars. Use standard format unless your system requires something else.

Question 10

How does the UUID Inspector work?

Accepted Answer

Paste any UUID. It shows version, variant, and for time-based UUIDs, the embedded timestamp. Field breakdown with color-coding. Useful for debugging and understanding UUID structure.

UUID Generator & Toolkit

How to Use

Frequently Asked Questions

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