UUID, ULID & Nano ID generator — offline

Identifiers generated by a website are identifiers that website has seen. For most throwaway uses that is harmless, but developers routinely generate IDs that become API keys, tenant identifiers, invitation tokens, or database primary keys in production — and those should not exist in a stranger's request log before they exist in your system.

Every value here comes from your browser's cryptographically secure random generator — crypto.randomUUID and crypto.getRandomValues — running on your device. There is no backend to log anything, and a Content-Security-Policy blocks third-party requests. Nobody else ever sees these values, and you can generate them with the network disconnected.

v4 is 122 bits of pure randomness. It is the safe default when an identifier must reveal nothing at all — no creation time, no ordering, no correlation between two IDs issued moments apart.

v7 (standardised in RFC 9562) begins with a millisecond timestamp and fills the rest with randomness. Because the leading bits increase over time, v7 values sort by creation order as plain strings. That is a significant practical advantage for database primary keys: random v4 keys scatter inserts across a B-tree index, fragmenting pages and hurting write performance, while time-ordered keys append near the end where the pages are already warm.

The trade-off is that a v7 identifier discloses roughly when it was created. Use v7 for internal primary keys, v4 for anything user-facing or security-sensitive.

• ULID — 26 characters in Crockford base32, also time-sortable. It is case-insensitive, avoids the letters that look like digits, and is noticeably friendlier than a UUID when a human has to read one aloud or type it from a screen.
• Nano ID — compact and URL-safe, the sensible pick for short links, public slugs, and anywhere a 36-character UUID would dominate the URL. Shorter means fewer random bits, so use it where the identifier is a lookup key rather than a secret.

Generate up to 1,000 at a time as a newline-separated list, which is what you want for seeding a test database or filling a fixture file. Related and equally local: password generator for secrets rather than identifiers, hash generator for deterministic fingerprints, and mock data generator for whole test records.