How to generate UUIDs
- Enter how many UUIDs you need, from 1 to 100. Values outside that range are corrected automatically.
- Optionally tick Uppercase or Remove hyphens to match the format you need. Changing either option generates a fresh batch, so choose your format before copying.
- Click Generate for a new batch, then Copy all to copy the list, one UUID per line.
What is a version 4 UUID?
A UUID (universally unique identifier, also called a GUID) is a 128-bit value written as 32 hexadecimal digits in five groups, 8-4-4-4-12, for 36 characters including hyphens. Version 4 UUIDs are built from random data: 122 of the 128 bits are random, and the other six bits mark the version and variant. You can see both in 550e8400-e29b-41d4-a716-446655440000: the first digit of the third group is always 4 (the version), and the first digit of the fourth group is always 8, 9, a or b (the variant). If you spot those two markers, a string is shaped like a valid v4 UUID.
Will two UUIDs ever collide?
Practically, no. With 122 random bits there are about 5.3 × 1036 possible v4 UUIDs. By the birthday paradox, you would need to generate roughly 2.7 × 1018 of them for a 50% chance of one duplicate, which is about a billion per second for 85 years. Even a one-in-a-billion chance needs around a hundred trillion UUIDs. The main real-world cause of duplicates is not bad luck but a poor random source, or copying the same value by accident. This tool takes its randomness from the browser's secure random generator, using crypto.randomUUID() when available.
Where UUIDs are used
- Database keys: records can be created on many servers or in an offline app and merged later without ID clashes.
- API and log tracing: a request ID that follows one operation across several services.
- File and upload names: prevents two users’
image.jpgfrom overwriting each other. - Test data and fixtures: developers and QA testers generate a batch of IDs for mock records.
Formats and variations
Case does not matter for a UUID. The standard says they are case-insensitive when read, and lowercase is the usual output, while some tools, especially on Windows, show uppercase. Removing hyphens gives a 32-character string, which is common in URLs and some databases. This generator does not add the curly braces that some Microsoft formats use; add them yourself if a system needs them. Only version 4 is produced here. Other versions exist: v1 uses a timestamp and machine details, v3 and v5 hash a name, and v7, defined in the 2024 UUID standard RFC 9562, puts a timestamp first so that new IDs sort in creation order.
Tips and common mistakes
- Database performance: fully random v4 keys scatter inserts across an index, which can slow large tables compared with sequential IDs. Store UUIDs in a native 16-byte type if your database has one, instead of a 36-character string.
- Do not treat a UUID as a password. It is hard to guess, but IDs end up in URLs, logs and referrer headers. Use a password generator or proper tokens for secrets.
- Do not shorten them. Cutting a UUID to the first 8 characters leaves only 32 bits, and collisions become realistic after tens of thousands of IDs.
- Copy before changing options. Toggling Uppercase or Remove hyphens replaces the list with new values rather than reformatting the old ones.
Limits of this tool
Up to 100 UUIDs per batch, version 4 only, with no namespace or timestamp variants. Generated values are not saved anywhere, so copy what you need before leaving the page.
Is it private and safe?
Yes. Every UUID is generated with the Web Crypto secure random generator, entirely on your device. Nothing is ever uploaded, stored or transmitted, and the page works even offline once loaded.
Related guides
Learn more in what is a UUID, create secrets with the password generator, or fingerprint data with the hash generator.
Frequently asked questions
What is a UUID and what does v4 mean?
A UUID is a 128-bit identifier written as 36 characters in an 8-4-4-4-12 pattern. Version 4 means it is generated from random data rather than from a timestamp or hardware address. The digit 4 at the start of the third group marks the version.
Can two generated UUIDs collide?
A v4 UUID has 122 random bits, so about 5.3 x 10^36 values exist. You would need roughly 2.7 x 10^18 UUIDs for a 50% chance of a single duplicate. For ordinary applications, collisions are not a practical concern.
Are UUID and GUID the same thing?
In practice yes. GUID is the name Microsoft uses for the same 128-bit identifier format. Version 4 GUIDs and UUIDs are interchangeable, apart from cosmetic differences like uppercase letters or curly braces.
Why does the fourth group always start with 8, 9, a or b?
Those two leading bits of that group are reserved to mark the UUID variant defined by the standard, leaving 14 random bits. Together with the fixed 4 in the third group, that is why 122 of the 128 bits are random.
Should I use UUIDs as passwords or secret tokens?
No. They are unpredictable, but they are designed as identifiers, and identifiers often leak into URLs, logs and analytics. Use a dedicated password or token generator for anything that grants access.
Are the UUIDs generated locally?
Yes. They are created in your browser with its secure random generator, using crypto.randomUUID() where available. Nothing is uploaded, stored or transmitted.
Why do the UUIDs change when I tick Uppercase?
Changing either option triggers a new generation instead of reformatting the existing list. Set Uppercase and Remove hyphens first, then generate and copy.
Is it free?
Yes, completely free with no sign-up. Each batch can contain up to 100 UUIDs, and you can generate as many batches as you like.