Frequently Asked Questions
Everything you need to know about the UUID / ULID Generator.
What is a UUID?
A UUID (Universally Unique Identifier) is a 128-bit label used to uniquely identify information in computer systems. It is formatted as 32 hexadecimal digits separated by hyphens in the pattern 8-4-4-4-12, for example 550e8400-e29b-41d4-a716-446655440000. UUIDs are standardised in RFC 4122.
What is the difference between UUID v4 and UUID v7?
UUID v4 is entirely random — all 122 bits are generated from a cryptographically secure random source. UUID v7 embeds a 48-bit Unix millisecond timestamp in the most-significant bits, making IDs monotonically increasing and database-index-friendly. Use v4 when order does not matter; use v7 as database primary keys where sorted inserts improve B-tree performance.
What is a ULID?
A ULID (Universally Unique Lexicographically Sortable Identifier) encodes a 48-bit millisecond timestamp and 80 random bits into a 26-character Crockford Base32 string. It is URL-safe, case-insensitive, and sorts lexicographically by creation time — making it a compact alternative to UUID v7 when human readability and sortability both matter.
Are the generated IDs truly unique?
UUID v4 has 122 random bits, giving a collision probability so small it is negligible for any practical application — you would need to generate billions of IDs per second for thousands of years before expecting a collision. UUID v7 and ULID add a timestamp prefix which further reduces collision risk within the same millisecond window. All generation uses the Web Crypto API, which provides cryptographically secure randomness.
Is this free to use?
Completely free. No sign-up, no account, no rate limits. Generate as many IDs as you need.
Are the IDs sent to a server?
No. Every ID is generated locally in your browser using the Web Crypto API. Nothing is sent to any server. The generated values never leave your device.
What does uppercase / lowercase do?
UUIDs use hexadecimal characters (0–9, a–f). The uppercase option converts hex letters to A–F; lowercase keeps them as a–f. Both are valid UUID representations. ULIDs are always uppercase Crockford Base32, so the case toggle is hidden when ULID mode is active.
How do I copy all generated IDs at once?
Click the Copy All button above the list. It copies every ID to the clipboard as a newline-separated list, ready to paste into code, a spreadsheet, or a database seeding script.
What is the maximum number of IDs I can generate at once?
You can generate up to 100 IDs in a single batch. Set the Count field to any value from 1 to 100 and click Generate.
When should I use UUID v7 instead of v4?
Use UUID v7 as primary keys in relational databases. Because v7 IDs are time-ordered, new rows insert at the end of the B-tree index rather than in random positions, which dramatically reduces page splits and improves write performance at scale. UUID v4 is fine for identifiers where insertion order does not affect performance.