UUID Generator
Generate cryptographically secure UUIDs (v4), timestamp-based UUIDs (v1), and bulk UUIDs instantly.
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What is a UUID?
A UUID (Universally Unique Identifier) is a 128-bit label used to uniquely identify objects in computer systems. Also called a GUID (Globally Unique Identifier) in Microsoft contexts, UUIDs are standardised by RFC 4122.
What is UUID v4?
UUID v4 is randomly generated using a cryptographically secure random number generator. It has 122 bits of randomness, giving a probability of collision so low it is effectively impossible in practice.
What is the difference between v1 and v4?
UUID v1 is based on the current timestamp and a node identifier (usually derived from a MAC address). UUID v4 is entirely random. v4 is preferred when privacy matters; v1 is useful when chronological ordering is needed.
What are UUIDs used for?
Database primary keys, session tokens, filenames, API keys, message IDs, distributed system identifiers, and anywhere a globally unique label is needed without a central registry.
About the UUID Generator
Our free UUID generator creates version 4 UUIDs (Universally Unique Identifiers) instantly in your browser. UUIDs are 128-bit identifiers formatted as 32 hexadecimal digits in the pattern xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx. They are used throughout software development as unique keys for database records, session tokens, API identifiers, file names, and distributed systems where uniqueness must be guaranteed without central coordination.
The probability of generating a duplicate UUID is so astronomically small (1 in 5.3×10³⁶) that it is considered practically impossible. This is why UUIDs are the standard choice for unique identifiers in modern software systems.
UUID Version 4 Explained
Version 4 UUIDs are randomly generated. The "4" in the third group indicates the version, and the first digit of the fourth group is either 8, 9, a, or b to indicate the variant. All other 122 bits are random. This means each UUID generated is unique with overwhelming probability, making version 4 the most commonly used UUID type for general purposes.
Common Uses for UUIDs
- Database primary keys — Use UUIDs instead of sequential integers to avoid key conflicts in distributed databases and when merging records from multiple sources.
- REST API identifiers — Assign UUID identifiers to API resources for globally unique, non-guessable resource IDs.
- Session tokens — Generate unique session identifiers for web application user sessions.
- File naming — Give uploaded files UUID-based names to prevent collisions and avoid exposing sequential structure.
- Microservices — Correlate log entries and events across distributed services using a UUID trace ID.
- Testing and development — Generate realistic-looking test data with proper UUID fields.
- Blockchain and DeFi — Create unique identifiers for smart contract interactions and off-chain records.
How to Generate a UUID
- Click Generate UUID — A fresh UUID appears instantly.
- Generate multiple UUIDs — Set the count field to generate batches of 1 to 100 UUIDs at once.
- Copy to clipboard — Click any UUID to copy it, or use "Copy All" for batch results.
- Choose format — Standard format with hyphens, or compact format without hyphens for storage efficiency.
Frequently Asked Questions
Are generated UUIDs truly unique?
Version 4 UUIDs have 122 random bits, giving 5.3×10³⁶ possible values. The probability of two UUIDs colliding is so small it is considered negligible for all practical applications.
Can I use UUIDs as database primary keys?
Yes. UUID primary keys are common in PostgreSQL, MySQL, MongoDB, and other databases. They allow records to be created without querying the database for the next available ID, which is valuable in distributed systems.
What is the difference between UUID v1 and UUID v4?
UUID v1 is time-based and includes the host machine's MAC address, which can expose information. UUID v4 is fully random and reveals no information about where or when it was generated.
Are the generated UUIDs saved anywhere?
No. UUID generation happens entirely in your browser using the Web Crypto API. No UUIDs are stored or transmitted to our servers.