A UUID (universally unique identifier) is a 128-bit value written as 32 hexadecimal digits in five groups, such as the familiar 8-4-4-4-12 layout. Developers use UUIDs whenever they need an ID that will not clash with anyone else's, without asking a central database for the next number. Microsoft calls the same thing a GUID.
This tool generates version 4 UUIDs, the fully random kind defined in RFC 4122. Each one uses Web Crypto randomness from your browser, with the version and variant bits set exactly as the standard requires. Generate a single ID for a quick test or up to 1,000 for seed data, fixtures and migration scripts, then copy them or download them as a plain text file.
How to use: UUID v4 Generator
- Enter the Number of UUIDs you need, from 1 to 1,000.
- Select Generate UUIDs.
- Review the list: each line holds one lowercase UUID v4.
- Select Copy to paste the IDs into your code, or Download to save them as a .txt file.
Example: Number of UUIDs 3 returns three lowercase v4 IDs in the 8-4-4-4-12 hex format, one per line.
What is a UUID, and how is version 4 built?
Of the 128 bits in a UUID v4, six are fixed: four mark the version (the first digit of the third group is always 4) and two mark the RFC 4122 variant (the first digit of the fourth group is always 8, 9, a or b). The remaining 122 bits are random. That fixed structure lets any parser recognize the value as a valid random UUID.
Version 4 contains no timestamp, MAC address or other information about where or when it was created, which also makes it a privacy-friendly choice for public-facing IDs.
UUID collision odds: can two ever match?
In theory yes, in practice no. With 122 random bits there are about 5.3 × 10^36 possible values. By the birthday-problem math, you would need to generate roughly 2.7 quintillion (2.7 × 10^18) UUIDs before the chance of even one duplicate reached 50 percent. Producing a billion per second, that would take around 86 years.
Those odds assume a high-quality random source. Weak generators based on Math.random are where real-world duplicates come from, which is why this tool relies on crypto.getRandomValues.
Where developers use bulk UUIDs
Version 4 is the default choice for most general-purpose identifiers:
- Primary keys in PostgreSQL (native uuid type) or MySQL and MariaDB (BINARY(16) or CHAR(36)).
- Seed data, test fixtures and mock API responses.
- Idempotency keys and request or correlation IDs in distributed systems.
- Unique file names for uploads, so two users never overwrite each other.
- GUIDs in .NET, SQL Server and Windows configuration files.
Frequently asked questions
What is the difference between a UUID and a GUID?
Practically none. UUID is the name used in RFC 4122 and most programming languages, while GUID is the name Microsoft adopted for the same 128-bit format. Some Microsoft tools display GUIDs in uppercase or wrap them in curly braces, but the underlying value is identical. The IDs generated here work wherever a GUID is expected.
Are these UUIDs truly unique?
They are unique for every practical purpose. Each one carries 122 random bits from the browser's cryptographically secure generator, and you would need around 2.7 quintillion of them for a 50 percent chance of a single repeat. If your system must guarantee uniqueness absolutely, add a unique constraint in the database, which is good practice anyway.
Can I generate UUID v1 or v7 here?
No. The tool only produces random version 4 UUIDs. If you need time-ordered IDs that sort by creation time, such as UUID v7, use your database or programming language: PostgreSQL 18 includes a uuidv7 function, and current UUID libraries for most languages support it. For general-purpose identifiers, v4 is perfectly adequate.
Are the UUIDs uppercase or lowercase?
They are lowercase, which is the canonical form recommended by the standard and expected by most systems. UUID comparisons are normally case-insensitive, so uppercase versions refer to the same value. If a tool you use requires uppercase, convert the list in your editor or with a case converter before pasting it in.
Is it safe to use UUIDs as secret tokens?
A v4 UUID is hard to guess, but it was designed as an identifier, not a secret. It often ends up in URLs, logs and error messages where secrets should not live. For password reset links, API keys or session tokens, use a dedicated token generator in your framework that is built for that purpose.