UUID Generator
Generate v4 UUIDs in bulk, with randomness from the browser's cryptographic API.
Prefer crypto.randomUUID(); if the browser doesn't support it, falls back to crypto.getRandomValues() Assembled by hand, but still random enough to meet the v4 spec.
When to use it
- You need primary keys for fixtures, CSV rows or a seeded table: generate 50 at once and paste them straight into INSERT statements, with no uuidgen install and no command per row.
- You need a request ID, idempotency key or idempotency token that leaks neither time nor machine identity: v4 is all random bits, unlike v1, which encodes a timestamp and a MAC address.
When not to
- You plan to sort by primary key or paginate by creation time. v4 is random, so inserts scatter across the B-tree and the ID says nothing about order; use UUID v7, ULID, or an auto-increment column plus a timestamp.
- The same name must always map to the same ID (idempotent imports, deterministic fixtures). That is a v3 (MD5) or v5 (SHA-1) namespace UUID; this tool only produces v4, so every click is a new value.
Generation happens entirely in the browser; nothing is uploaded or stored. It prefers crypto.randomUUID and falls back to getRandomValues with the version bits written manually. Limits: v4 only, no v1/v3/v5/v7; at most 100 per click; no check against IDs you already have; randomUUID needs a secure context (HTTPS or localhost).
Frequently asked
Can two v4 UUIDs collide?
In theory yes; the probability is negligible — 122 random bits, roughly 10^-19 even across a billion values. Real duplicates almost always come from engineering, not mathematics: independent generators per host, retried inserts, truncated copy-paste. Keep a unique index in the database and treat it as the actual guarantee instead of trusting that it probably will not collide.
Can I store the uppercase form?
You can, but be consistent. RFC 9562 specifies lowercase output and case-insensitive comparison, yet many database collations, Redis keys and log searches are case-sensitive, so mixing the two means looking up the same UUID fails. Store and transmit lowercase, and convert to uppercase only for display or for older systems that demand it (some Oracle and SAP interfaces).
Does a UUID reveal when or where it was generated?
Not v4: apart from the version and variant bits it is pure randomness, with no timestamp and no node identifier. Other versions do leak: v1 carries the creation time and the NIC's MAC address (or a random node), and v7 carries a millisecond timestamp. This tool generates v4 only, so that inference is impossible — but it also cannot serve as a time-ordered ID.