Bulk UUID v4 Generator for Testing
Generate UUID v4 and GUID values in bulk using browser crypto for tests, mock data, primary keys, and API fixtures.
Written by Anil Gautam · Updated
What do the parts of a UUID v4 mean?
A UUID is 128 bits written as 32 hexadecimal digits in groups of 8, 4, 4, 4 and 12: 36 characters with hyphens, or 32 with Hyphens cleared. Version 4 fixes six of those bits. The first digit of the third group is always 4, and the first digit of the fourth group is 8, 9, a or b. In 363200f7-25ae-4b48-96f4-6ebe7b1eb15d, those are the 4 of 4b48 and the 9 of 96f4. The other 122 bits come from your browser's cryptographic random generator, through crypto.randomUUID or crypto.getRandomValues.
UUIDs are case-insensitive when read, and the standard asks for lowercase output, so leave Uppercase off unless the system you paste into expects capitals. GUID is Microsoft's name for the same 128-bit format, so these values work where a GUID is expected; the tool does not add the curly braces some Windows tools show around them.
Can two generated UUIDs be the same?
A repeat is possible, and the odds are tiny. With 122 random bits there are about 5.3 × 10^36 possible values. By the birthday bound, a 50 percent chance of any repeat needs about 2.7 × 10^18 UUIDs, roughly a billion per second for 86 years, and a set of one billion has a collision chance near 9.4 × 10^-20.
In test data, a repeated ID is far more likely to come from pasting the same list twice. Any change to Type, Count, Hyphens or Uppercase generates a fresh list, so copy what you need before toggling an option. Count accepts 1 to 100, and Copy all puts one ID per line, ready for a spreadsheet column.
Should you use NanoID or UUID v4?
NanoID builds 21 characters from a 64-symbol alphabet of A to Z, a to z, 0 to 9, underscore and hyphen, giving 126 random bits in a shorter, URL-safe string. Each random byte is masked to 6 bits, and since 256 is a multiple of 64, every symbol is equally likely. Keep Uppercase off for NanoIDs: it merges the 52 letters into 26, which cuts the randomness to about 109 bits and can turn two different IDs into the same one.
Random v4 keys arrive in no particular order, which scatters inserts across a database index. If you need IDs that sort by creation time, RFC 9562 defines UUID version 7; this tool generates only v4 and NanoID. For realistic names, emails and addresses in fixtures, use the Fake Data Generator.