A UUID generator is a free online developer tool that instantly creates cryptographically secure Version 4 UUIDs — universally unique identifiers — one at a time or in bulk, with one-click copy to clipboard. UUID stands for Universally Unique Identifier — a 128-bit label used to uniquely identify information in computer systems, guaranteed to be globally unique without any central coordination, registry, or communication between the generating systems.
A UUID is a 128-bit value represented as 32 hexadecimal digits grouped into five sections separated by hyphens:
xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx
Example: f47ac10b-58cc-4372-a567-0e02b2c3d479
| Section | Length | Bits |
|---|---|---|
| time_low | 8 hex chars | 32 bits |
| time_mid | 4 hex chars | 16 bits |
| time_hi_and_version | 4 hex chars | 16 bits |
| clock_seq | 4 hex chars | 16 bits |
| node | 12 hex chars | 48 bits |
| Total | 32 hex chars | 128 bits |
In a v4 UUID, the version digit (first character of the third group) is always 4, and the variant digit (first character of the fourth group) is always one of {8, 9, a, b}. Everything else is cryptographically random.
| Version | Algorithm | Sortable | Deterministic | Privacy Safe | Recommended For |
|---|---|---|---|---|---|
| v1 | Timestamp + MAC | ✅ Yes | ❌ No | ❌ No | Cassandra, time-ordered systems |
| v3 | MD5 name-based | ❌ No | ✅ Yes | ✅ Yes | Legacy name-based (avoid MD5) |
| v4 | Random (CSPRNG) | ❌ No | ❌ No | ✅ Yes | General purpose — default choice |
| v5 | SHA-1 name-based | ❌ No | ✅ Yes | ✅ Yes | Name-based identifiers |
| v7 | Unix timestamp + random | ✅ Yes | ❌ No | ✅ Yes | Modern DB primary keys |
A UUID v4 uses 122 bits of random data. The number of possible UUID v4 values is 2^122 ≈ 5.3 undecillion — that is 5.3 × 10^36 possible values.
To reach a 50% probability of at least one collision, you would need to generate approximately 2.71 quintillion UUIDs. If every person alive on Earth (8 billion people) generated one UUID every second continuously, it would take approximately 10 billion years before there was a 50% chance of a single collision occurring. In any practical software system, UUID v4 collisions are not a realistic concern.
UUIDs as primary keys provide: distribution-safe (multiple app instances generate keys without coordination), privacy-protecting (sequential IDs expose record counts — /users/1547 reveals at least 1,547 users; UUIDs reveal nothing), and merge-friendly (records from different databases can be merged without ID conflicts).
Every resource in a REST API needs a unique identifier in its URL: GET /api/users/f47ac10b-58cc-4372-a567-0e02b2c3d479
APIs that process payments or send emails use idempotency keys to ensure retried requests are not processed twice. The client generates a UUID, sends it with the request, and the server uses it to deduplicate.
In microservices architectures, a UUID generated at the API gateway and passed through every internal call allows all log entries across all services for a single user request to be correlated and assembled into a complete trace.
Developers generating test data — seeding databases, creating mock API responses, writing unit test fixtures — need unique identifiers for every test record. A bulk UUID generator produces dozens or hundreds of UUIDs instantly.
Yes. This online UUID generator is 100% free with no registration, no subscription, and no payment required. Generate as many UUIDs as you need, individually or in bulk.
Yes. This generator uses the browser's crypto.getRandomValues() API — a cryptographically secure pseudo-random number generator (CSPRNG) seeded from genuine hardware entropy. The generated UUIDs are suitable for use as session tokens, API keys, password reset tokens, and other security-sensitive identifiers.
UUID v4 uses 122 bits of cryptographically random data with no structure — fully random and not sortable by generation time. UUID v7 encodes a Unix millisecond timestamp in the most significant bits followed by random bits — making it both unique and chronologically sortable. UUID v7 is increasingly preferred for database primary keys because its time-ordered nature improves index performance compared to random v4.
Theoretically yes — collisions are possible. Practically no — the probability is so astronomically low that it is treated as zero in engineering. To have a 50% probability of a single collision, you would need to generate approximately 2.71 quintillion UUIDs.
Functionally yes. GUID (Globally Unique Identifier) is Microsoft's term for the same concept. GUIDs follow the UUID specification (RFC 4122) and are structurally identical. The terms UUID and GUID are used interchangeably in most contexts.
UUID v4 is widely used and works well for most applications. The main consideration is index performance — UUID v4's random ordering can cause index fragmentation in MySQL InnoDB. Solutions include using UUID v7 for monotonically increasing UUIDs, using PostgreSQL's native UUID type (which handles this well), or using a sequential integer primary key with UUID as a secondary unique index for external exposure.
No. UUID generation happens entirely within your browser using the Web Crypto API (crypto.getRandomValues()). No generated UUIDs, no input data, and no usage information is transmitted to any server or logged anywhere.
Use our free Free Online UUID Generator — no signup, no download, works instantly on any device.
Open Free Online UUID Generator — Free →