Question 1

What is the difference between UUID v4 and UUID v7?

Accepted Answer

UUID v4 is entirely random — 122 random bits, universally unique, but not sortable by creation time. UUID v7 (RFC 9562) embeds a 48-bit millisecond timestamp in the first six bytes, making rows naturally sortable by insertion time and dramatically improving B-tree index performance. v7 is the recommended choice for database primary keys in 2024+.

Question 2

Why should I use UUID v7 as a database primary key instead of v4?

Accepted Answer

Random v4 UUIDs cause fragmentation in B-tree indexes — every insert goes to a random page, forcing expensive page splits and making the index balloon in size. v7 UUIDs sort monotonically (new IDs always append to the right of the B-tree), which is equivalent to using an auto-increment integer while still being globally unique and safe to generate client-side without a sequence.

Question 3

What is a ULID?

Accepted Answer

ULID (Universally Unique Lexicographically Sortable Identifier) encodes a 48-bit timestamp and 80 random bits as 26 Crockford Base32 characters. Like UUID v7 it's timestamp-sortable, but it's shorter, has no dashes, and uses a case-insensitive alphabet that avoids ambiguous characters (0, O, I, L). ULIDs sort correctly as plain strings in any database column.

Question 4

What is NanoID and when should I use it?

Accepted Answer

NanoID generates 21 URL-safe characters (A-Z, a-z, 0-9, _, -) with 126 bits of entropy. It's smaller than a UUID when stored as a string, URL-friendly without encoding, and a good choice for short link IDs, session tokens, or any identifier that appears in a URL.

Question 5

Can I decode a UUID to find out when it was created?

Accepted Answer

Yes — for UUID v7 and ULID, the timestamp is embedded directly in the identifier. Paste one into the Validate tab and the tool will extract the exact millisecond it was created. For UUID v4, no timestamp exists — all bits are random.

Question 6

What do the format options mean?

Accepted Answer

Standard is lowercase with dashes (the default). UPPERCASE is the same with capital letters. No dashes removes the hyphens (useful for some databases). Braces wraps in {} (Microsoft-style). URN prefixes with urn:uuid: (for URN namespaces). SQL wraps in single quotes for direct use in INSERT statements.

Question 7

Is this generator cryptographically secure?

Accepted Answer

Yes. All randomness comes from crypto.getRandomValues() — the same Web Cryptography API used by password managers and TLS. This is a CSPRNG (cryptographically secure pseudo-random number generator) and is suitable for security-sensitive identifiers.

Format	Length	Sortable	Best for
UUID v4	36 chars	✗ Random	General use, distributed systems
UUID v7	36 chars	✓ By time	Database PKs, event IDs, logs
ULID	26 chars	✓ By time	DBs, sorting as plain strings
NanoID	21 chars	✗ Random	URLs, session IDs, short links

UUID Generator

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