UUID Generator

UUID Generator creates universally unique identifiers — UUIDs, also called GUIDs — in version 4 format. Generate a single UUID or hundreds at once, copy them individually or all together, and use them in your database schema, code, API payloads, or any system requiring globally unique identifiers. All generation happens in your browser using a cryptographically secure random number generator — no server required.

A UUID (Universally Unique Identifier) is a 128-bit number standardised by RFC 4122, displayed as 32 hexadecimal characters arranged in the pattern xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx (for example, 550e8400-e29b-41d4-a716-446655440000). The 128-bit size allows 2^128 possible values — approximately 3.4 × 10^38 — a number so immense that generating UUIDs randomly has a practically zero probability of collision. GUID (Globally Unique Identifier) is Microsoft's terminology for the same format and is interchangeable with UUID.

UUID v4 is the most widely used version. It is entirely randomly generated — 122 bits of random data with 6 bits reserved for the version (0100) and variant fields. Because generation requires no coordination between systems, any machine anywhere can generate a v4 UUID independently and be confident it will not collide with UUIDs generated by any other machine. Other versions include: v1 (time-based, encodes the machine's MAC address and current timestamp — not recommended for privacy-sensitive applications), v3 and v5 (deterministic, derived from a namespace and name using MD5 or SHA-1 hashing), and v7 (time-ordered, monotonically increasing — useful for database index performance).

The primary use of UUIDs in software development is as primary keys for database records. Traditional auto-incrementing integer IDs have limitations that UUIDs solve. Integer IDs are sequential and predictable — knowing your user ID is 1042 makes it trivial to guess that 1043 also exists (enumeration attack). Integer IDs reveal business scale — an order ID tells a competitor how many orders you have processed. Integer IDs require a central coordinator — merging two databases with overlapping ID ranges requires reassigning IDs. UUID primary keys are non-enumerable, reveal no business information, and work across distributed systems without central coordination.

UUIDs are used as identifiers well beyond database primary keys. Session tokens and CSRF tokens use UUID-like random values for unpredictability. Idempotency keys in payment APIs ensure a request processed twice with the same key executes only once. Message IDs in event-driven systems identify individual events. File names for uploaded user content use UUIDs to prevent collisions. Feature flag and A/B test variant IDs use UUIDs. Correlation IDs passed through distributed microservice calls for tracing use UUID format.

The probability of a UUID v4 collision is often cited but rarely understood. To have a 50% probability of a single collision, you would need to generate approximately 2.71 × 10^18 UUIDs — roughly 2.71 quintillion. At 1 billion UUIDs generated per second, reaching this collision probability would take about 86 years. In any realistic application generating millions or even billions of UUIDs, collision is not a concern you need to design around.

UUID Generator runs entirely in your browser using JavaScript's crypto.randomUUID() method in modern browsers, falling back to the WebCrypto API's getRandomValues() for compatibility. Both methods produce cryptographically random UUIDs meeting RFC 4122 v4 requirements. Generated UUIDs are never transmitted to any server. Bulk generation of hundreds of UUIDs is supported for seeding test databases and generating batch identifiers.