UUID Generator
Generate any number of v4 UUIDs.
UUIDs are generated entirely in your browser — never uploaded or stored.
What is this tool?
The UUID generator creates random UUID v4 values instantly — handy for database primary keys, API resource IDs, session tokens, or temporary filenames that need to be unique. Set a count and options, then press Generate.
Options
- Count: generate 1 to 100 UUIDs at once.
- Uppercase: lowercase (RFC 4122) by default; enable to display all uppercase.
- Include hyphens: disable to output a continuous 32-character string without
-.
crypto.randomUUID() or crypto.getRandomValues() for cryptographically strong randomness.
Privacy & processing
Everything runs in your browser. Results are never uploaded or stored, and you can copy them all to your clipboard.
UUID v4's 128-bit layout — where the version and variant bits sit
A UUID v4 represents 128 bits as 32 hex digits (36 characters including 4 hyphens). Of those, 4 bits are a fixed version marker and 2 bits are a fixed variant marker — only the remaining 122 bits are random. Looking at this tool's actual generator code, bytes[6] = (bytes[6] & 0x0f) | 0x40 fixes the top 4 bits of byte 7 to 0100 (version 4), and bytes[8] = (bytes[8] & 0x3f) | 0x80 fixes the top 2 bits of byte 9 to 10 (RFC 4122 variant). In the resulting xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx layout, the first character of the third group is always 4, and the first character of the fourth group (y) is always one of 8, 9, a, or b.
How big is the collision odds, and v4 vs v7
122 bits of randomness means 2^122 ≈ 5.32×10^36 possible combinations. Using the birthday-paradox approximation, reaching a 50% chance of any collision takes roughly 2.71×10^18 UUIDs (2.71 quintillion). Even generating a billion per second nonstop, that would take about 86 years. No real-world system comes close to that volume, so v4 is treated as unique for all practical purposes.
Meanwhile, the newer UUID v7 standard embeds a millisecond timestamp up front, producing UUIDs that sort chronologically. v4's pure randomness means database index inserts land at scattered positions, hurting B-tree index performance, while v7's ordered generation avoids that. But because v7 exposes its creation time, v4 remains the better choice when you need to hide timing information. This tool only supports v4, the most widely used version.