UUID generator (v4, v7) and validator

Generate up to 1000 UUIDs at once (random v4 or time-ordered v7), or paste a UUID to check that it is valid and see its version, variant and timestamp.

🔒 Runs entirely in your browser. Nothing you paste is uploaded or sent to a server.

v4 or v7?

UUID v4 is 122 random bits. It is the default almost everywhere (crypto.randomUUID(), Python uuid.uuid4(), Postgres gen_random_uuid()). Use it when the ID must reveal nothing.

UUID v7 (RFC 9562, 2024) starts with a 48-bit Unix timestamp in milliseconds, followed by random bits. New IDs sort after old ones, so they behave much better as database primary keys: inserts go to the end of a B-tree index instead of random pages, which keeps indexes smaller and inserts faster in Postgres and MySQL. The trade-off: anyone can read the creation time from the ID. This tool's v7 generator adds a counter so that even IDs created in the same millisecond are strictly increasing.

The generator uses your browser's cryptographically secure random source (crypto.getRandomValues / crypto.randomUUID), never Math.random.

Anatomy of a UUID

xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx: 32 hex digits in groups of 8-4-4-4-12. M is the version (1-8). N is the variant: 8, 9, a or b means a standard RFC 9562 UUID; c/d is a legacy Microsoft GUID. The nil UUID (all zeros) and max UUID (all f) are special values.

Common problems

• "not a valid UUID": usually braces, a urn:uuid: prefix, whitespace or a truncated copy. The validator accepts and strips braces and prefixes, and points to the first invalid character.
• Case: UUIDs are case-insensitive, but string comparison in code is not. Normalize to lowercase before comparing or storing as text.
• JSON: Python's json.dumps cannot serialize uuid.UUID objects; convert with str(u).
• Storage: store UUIDs in a native uuid column (Postgres) or BINARY(16) (MySQL), not VARCHAR(36).

Last updated 2026-11-05.