A UUID (Universally Unique Identifier) — also known as GUID (Globally Unique Identifier in Microsoft terminology) — is a 128-bit number used to uniquely identify information across computer systems. UUIDs are standardized by the RFC 4122 specification and are widely used in databases, distributed systems, and software development.

UUID v4 is a randomly generated UUID variant. Out of the 128 bits, 122 bits are generated using a cryptographically strong random number generator (CSPRNG). The remaining 6 bits are reserved: 4 bits indicate version 4, and 2 bits indicate the RFC 4122 variant. This makes UUID v4 the most commonly used type for general-purpose unique identification.

UUID v4 has 2¹²² possible values (approximately 5.3 × 10³⁶). The probability of collision is astronomically small. To have a 50% chance of a single collision, you'd need to generate approximately 2.71 × 10¹⁸ UUIDs. For context, generating 1 billion UUIDs per second would take about 86 years to reach that number. For all practical purposes, UUID v4 collisions can be considered impossible.

UUID (Universally Unique Identifier) and GUID (Globally Unique Identifier) are essentially the same thing. GUID is Microsoft's term for UUID. Both follow the same 128-bit format and RFC 4122 specification. The terms are often used interchangeably in the industry.

The standard UUID format is 8-4-4-4-12 hexadecimal characters, separated by hyphens:
xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx
Where M indicates the UUID version (always 4 for v4), and N indicates the variant (always 8, 9, a, or b for RFC 4122). Some systems use UUIDs without hyphens (32 characters), which this tool also supports.

UUIDs as primary keys have pros and cons. Pros: global uniqueness (great for distributed systems), no reliance on a central sequence generator, and they don't reveal record counts. Cons: larger storage (16 bytes vs 4-8 bytes for integers), less efficient indexing in some databases due to randomness, and slightly slower join operations. For PostgreSQL, consider using UUID type natively. For MySQL, be aware that random UUIDs can cause B-tree index fragmentation.

This tool uses the browser's built-in crypto.getRandomValues() API — a cryptographically secure pseudo-random number generator (CSPRNG) — to generate truly random UUID v4 identifiers. All generation happens locally in your browser; no data is ever sent to any server. The tool sets the version nibble to 4 and the variant bits to 10xx (binary) as required by RFC 4122.

UUID v4 is generated from random data and does not contain any identifying information (unlike UUID v1 which includes MAC addresses and timestamps). However, UUIDs should not be used as security tokens or secrets. While the random source is cryptographically strong, UUIDs are designed for uniqueness — not for secrecy. For authentication tokens, use dedicated libraries that generate cryptographically secure random strings of appropriate length (e.g., 256+ bits).

Yes! This tool supports batch generation of up to 100 UUIDs at a time. Use the quantity selector or preset buttons (1, 5, 10, 25, 50) to choose how many you need. You can then copy individual UUIDs or use the "Copy All" button to copy all of them at once, separated by newlines. You can also download the batch as a .txt file.

UUID v1: Time-based, includes MAC address and timestamp. Sortable but reveals machine identity.
UUID v4: Random-based. Most widely used, no identifying info, but not sortable.
UUID v7: Time-ordered (Unix timestamp prefix + random suffix). Combines sortability of v1 with randomness of v4. Great for database indexes. Defined in the newer RFC 9562.
This tool generates UUID v4 — the most universal and widely compatible version.