GUID Generator: Create Random Version 4 GUIDs

How to use the guid generator

1. Set How many to the number of GUIDs you need (1 to 100).
2. Toggle Wrap in braces, Uppercase hex or Remove dashes to match your target format.
3. Click Generate to produce the identifiers.
4. Copy the results from the list below the button.

What is a version 4 GUID?

A GUID (Globally Unique Identifier) is a 128-bit value used to uniquely identify information in software systems. Version 4 GUIDs are generated entirely from random numbers, with a few fixed bits that indicate the version and variant. The format follows RFC 4122, which defines the layout as five groups of hexadecimal digits separated by hyphens: 8-4-4-4-12.

In a version 4 GUID, the 13th hex character is always 4 (the version nibble), and the 17th hex character is one of 8, 9, a or b (the variant bits). This guid generator uses crypto.getRandomValues to fill all 16 bytes with cryptographically strong randomness before setting those fixed bits.

Formatting options explained

Different platforms expect different GUID formats. Here is what each option does:

The underlying 128-bit value is identical regardless of formatting. Only the string representation changes.

How the randomness works

This tool allocates a 16-byte array and fills it using the Web Crypto API's getRandomValues method. That function draws from the operating system's cryptographic random number generator (such as /dev/urandom on Linux or CryptGenRandom on Windows).

After generating the raw bytes, two modifications enforce the version 4 specification:

1. Byte 6 has its top four bits cleared and set to 0100 (version 4): bytes[6] = (bytes[6] & 0x0f) | 0x40
2. Byte 8 has its top two bits set to 10 (RFC 4122 variant): bytes[8] = (bytes[8] & 0x3f) | 0x80

The resulting 16 bytes are then converted to 32 hexadecimal characters and split into the standard 8-4-4-4-12 grouping.

GUID vs UUID

GUID is Microsoft's term for the same concept defined as UUID (Universally Unique Identifier) in RFC 4122. In practice they are interchangeable. A version 4 GUID and a version 4 UUID have the exact same structure and generation method. When people search for a guid generator they are looking for the same thing as a uuid generator.

If you need to verify that an existing identifier conforms to the version 4 format, use the guid validator to check its structure, version nibble and variant bits.

Collision probability

A version 4 GUID contains 122 random bits (128 total minus 6 fixed bits for version and variant). That yields 2¹²² possible values, approximately 5.3 x 10³⁶. Using the birthday paradox approximation, you would need to generate about 2.7 x 10¹⁸ GUIDs before there is a 50 percent chance of a single collision.

To put that in perspective, generating one billion GUIDs per second would take roughly 85 years to reach that threshold. For any practical application, version 4 GUIDs can be treated as unique without a central registry.

When to use bulk generation

Generating multiple GUIDs at once is useful when seeding test databases, creating placeholder records or preparing configuration files. The bulk option produces up to 100 identifiers in a single click, each independently generated with fresh random bytes.

For security-sensitive applications like session tokens or API keys, consider whether a GUID is the right choice. While version 4 GUIDs have high entropy, dedicated tools like an API key generator may offer more appropriate encoding or length for authentication contexts.

Worked examples