Free UUID Generator Online

A UUID is a 128-bit identifier written as 32 hexadecimal characters split by 4 hyphens into an 8-4-4-4-12 pattern, like 550e8400-e29b-41d4-a716-446655440000. Its 1 job is to be unique without a central authority handing out numbers, so 2 services on opposite sides of a network can each mint an ID and trust the 2 will never collide. Standardized first as RFC 4122 in 2005 and refreshed as RFC 9562 in May 2024, the layout is deliberately dull: 4 bits mark the version, 2 bits mark the variant, and the remaining 122 bits carry either randomness or a timestamp depending on the version you choose.

The mistake that causes real damage is treating a UUID as a secret. A version 4 UUID holds 122 bits of randomness, roughly 5.3 × 10³⁶ combinations, which is ample entropy, yet the value still lands in URLs, access logs, referrer headers, emails, and browser history. Anyone who reads it can replay it. A UUID answers which record, not whether the caller may touch that record; the second question needs an authorization check on the server. Use a UUID as a primary key or an idempotency token, never as a password-reset link, session cookie, or API key on its own.

The text form is 36 characters, but the value is only 16 bytes, and that gap matters at scale. Stored as a CHAR(36) or VARCHAR(36) column a UUID costs 36 bytes plus overhead and compares character by character; stored as raw bytes it costs 16. MySQL has no native type, so the efficient pattern is BINARY(16) with the UUID_TO_BIN and BIN_TO_UUID helpers added in 8.0, and for v1 UUIDs the optional swap-flag reorders the timestamp for index locality. PostgreSQL ships a first-class uuid type that already stores 16 bytes and indexes cleanly. When a UUID must ride in a URL, base64url encoding shrinks the 36-character text to 22 characters with no data loss, dropping the 4 hyphens and the hex inflation. Across 100 million rows the CHAR(36) versus BINARY(16) choice alone is roughly 2 GB of table plus a larger index, so pick the compact form early rather than migrating later.

This generator runs entirely in your browser. It calls the native Web Crypto API for every value, so no identifier is sent to or logged by a server, and there is no network request to make. Pick v4 or v7, choose a display format among default, UPPERCASE, no-dashes, or the braced form that C# Guid and the Windows registry expect, and generate 1 or up to 10000 at once. What it does not do is register the IDs anywhere or test them against your database; uniqueness across your own tables is still your schema's job, and only a UNIQUE constraint or PRIMARY KEY can enforce it. A v4 value shows 4 as the 15th character and 8, 9, a, or b as the 20th; a v7 value shows 7 in that 15th slot, so you can eyeball which version you copied. Generation is instant even at the 10000 ceiling, since minting 1 UUID is 16 bytes of entropy and a few shifts, well under 1 millisecond. Treat these 36-character strings as ready-to-paste identifiers, not as proof of anything.