UUID Generator — Create Random UUIDs (v4) Online

This free UUID generator creates random version-4 UUIDs (Universally Unique Identifiers) using the browser's cryptographically secure crypto.randomUUID() API. A UUID is a 128-bit identifier with 122 bits of randomness, so the chance of two colliding is astronomically small — safe to treat as globally unique without any central coordinator. Generate one or bulk-generate up to 100 at once for database keys, session tokens, or filenames. Everything is generated locally in your browser, so the identifiers never leave your device.

Click Generate to create UUIDs

How UUIDs are generated

A UUID (Universally Unique Identifier) is a 128-bit identifier formatted as 32 hexadecimal digits in the pattern xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx, where M is the version and N is the variant. This tool generates version 4 UUIDs using the browser's crypto.randomUUID() API, which uses a cryptographically secure pseudorandom number generator (CSPRNG).

UUID v4 has 122 bits of randomness (6 bits are fixed for version and variant markers). The probability of two randomly generated UUIDs colliding is astronomically small: you would need to generate approximately 2.7 × 1018 UUIDs before reaching a 50% chance of a single collision. In practice, UUIDs are safe to treat as globally unique without any central coordination. They are widely used as primary keys in databases, filenames, session tokens, idempotency keys, and anywhere a unique identifier is needed without a central authority to issue sequential IDs.

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v4 random vs v7 time-ordered

The version-4 UUIDs this tool produces are fully random (122 bits of entropy). That randomness is great for uniqueness but terrible for database locality: consecutive inserts scatter across a B-tree index, fragmenting it and slowing writes on large tables. The newer version 7 UUID embeds a millisecond timestamp in its high bits, so values sort roughly in creation order while staying globally unique — increasingly the recommended choice for primary keys.

The collision maths, concretely

With 122 random bits, you'd need to generate about 2.7 × 10¹⁸ UUIDs before a 50% chance of any collision — billions per second for a century. For every practical purpose v4 is safe to treat as unique without coordination, which is precisely why distributed systems love it: no central ID server required.

Storage tips

Store UUIDs as 16-byte binary (BINARY(16) / uuid type), not as 36-character strings, to halve index size and speed lookups. Reserve the dashed text form for display and APIs.

⚠️ Common Mistakes to Avoid

Frequently asked questions

What is a UUID?

A 128-bit number used to uniquely identify information in computer systems.

Is a GUID the same as a UUID?

For most practical purposes, yes. GUID is Microsoft's term for the UUID standard.

Reviewed by the ToolsmithPro editorial team · Last updated June 2026. Every calculation and conversion runs entirely in your browser — your inputs are never uploaded, stored or shared. Formulas and methodology are documented on our about page; spot an error? tell us and we'll fix it.