UUID Generator

v4 is fully random — the everyday default when you just need an opaque unique id. v7 is time-ordered: its leading 48 bits are a Unix-millisecond timestamp, so v7 values sort in creation order. That makes v7 an excellent database primary key — new rows land at the right edge of a B-tree index instead of scattering like random v4, avoiding index fragmentation and page splits. The nilUUID is all zeros — a conventional placeholder meaning "no value".

Use v7 for new database primary keys and any id where sortable-by-creation-time helps (it keeps index writes fast and preserves rough ordering). Use v4 for opaque random tokens where you do not want any information leaked by the id. Use the nil UUID as a sentinel for "no id yet". Older v1 is time-based but embeds the machine MAC address and is generally only needed for legacy interop — this tool focuses on the two versions worth choosing today, v4 and v7, plus nil.

No — they are practically unique, not mathematically guaranteed. A v4 UUID has 122 random bits, so the probability of a collision is astronomically small: you would need to generate on the order of a billion UUIDs per second for about 85 years to reach a 50% chance of a single duplicate. For essentially every application this is safe to treat as unique, but the honest statement is "collision-resistant", not "impossible". v7 lowers collision odds further within a run by combining a timestamp with random bits.

The uniqueness and unpredictability of a UUID depend entirely on the quality of its random bits. This tool uses your browser's cryptographically secure random number generator — crypto.getRandomValues() and crypto.randomUUID() — which is designed to be unpredictable and evenly distributed. Math.random() is not cryptographically secure: its output can be predictable and is not intended for identifiers or tokens, which raises both collision and guessability risk. This generator never uses Math.random().

Yes. GUID (Globally Unique Identifier) is Microsoft's name for the same 128-bit identifier defined by RFC 9562; the two terms are interchangeable. The .NET and Windows world often writes them in braces and/or uppercase, for example {F47AC10B-58CC-4372-A567-0E02B2C3D479}. This tool offers braces and uppercase toggles so you can emit either the standard lowercase-hyphenated UUID form or the GUID style your platform expects.

No. Every UUID is generated entirely in your browser using the native Web Crypto API — nothing is uploaded, logged or stored, and the tool works offline once loaded. Bulk generation, copy and the .txt download all run on your device.