Free UUID Generator

UUID v4

Default choice for most applications. Database primary keys, session tokens, API keys — anywhere you need globally unique IDs without exposing a timestamp.

Best for: General purpose, REST APIs, database PKs

UUID v1

When you need to sort records by creation time without storing a separate timestamp. The embedded timestamp makes v1 IDs naturally ordered.

Best for: Event logs, audit trails, time-ordered records

UUID v5

When the same input must always produce the same UUID. Useful for generating stable IDs for known entities — e.g. a UUID for every known domain name.

Best for: Deterministic IDs, content hashing, idempotent operations

ULID

A drop-in replacement for UUID when lexicographic sorting matters. Stores as a 26-char string, encodes timestamp first — rows sort chronologically as strings.

Best for: Database PKs where sort order equals insert order

NanoID

When URL-safety and compactness matter. At 21 chars it has the same collision resistance as UUID v4 but is shorter and never needs URL encoding.

Best for: URL slugs, short codes, URL-safe IDs

What is a UUID?

A UUID (Universally Unique Identifier) is a 128-bit label used to uniquely identify information in computer systems. It is formatted as 32 hexadecimal digits in groups of 8-4-4-4-12 separated by hyphens, e.g. 550e8400-e29b-41d4-a716-446655440000.

What is the difference between UUID v1 and UUID v4?

UUID v1 is time-based, embedding the current timestamp and making IDs sortable by creation time. UUID v4 is completely random, offering better privacy since it reveals nothing about when or where it was generated. v4 is the most widely used format.

What is UUID v5 and when should I use it?

UUID v5 is deterministic — it generates a UUID by hashing a namespace UUID and a name string using SHA-1. The same namespace and name always produce the same UUID. This is ideal for generating stable IDs for known entities like domain names or product SKUs.

What is a ULID and how does it differ from a UUID?

A ULID (Universally Unique Lexicographically Sortable Identifier) encodes a millisecond timestamp in its first 10 characters, making it naturally sortable as a string. Unlike UUIDs, ULIDs sort in creation order — useful for database primary keys where chronological ordering matters without a separate created_at column.

Are the IDs generated client-side? Do they leave my browser?

Yes — all ID generation happens entirely in your browser using the Web Crypto API. No data is sent to any server, making this tool instantaneous and completely private.

What is the best free UUID generator?

ToolStack UUID Generator supports UUID v4, v1, v5, ULID, and NanoID — all free, no signup, 100% client-side. You can generate up to 100 IDs at once with formatting options including uppercase, no-hyphens, and braces. It is the most complete free UUID tool available.

Are UUIDs truly unique? Can two be the same?

UUID v4 has 122 bits of randomness, giving 2^122 possible values. The probability of generating a duplicate is astronomically small. For all practical purposes, UUIDs can be treated as globally unique identifiers.