Free UUID Generator — Generate v4 UUIDs Online

A UUID (Universally Unique Identifier) is a 128-bit identifier that is practically guaranteed to be unique across all systems, all time. The probability of generating two identical UUIDs is roughly 1 in 5.3 × 10^36 — you would need to generate 1 billion UUIDs per second for 85 years to have a 50% chance of a single collision.

Our free UUID generator creates cryptographically random v4 UUIDs using your browser's built-in crypto.getRandomValues() API. Generate single UUIDs or bulk batches for databases, APIs, testing, and development. No server, no signup, everything local.

What Is a UUID?

UUID stands for Universally Unique Identifier (also called GUID — Globally Unique Identifier, in Microsoft ecosystems). It is a standardized 128-bit number formatted as 32 hexadecimal digits displayed in five groups separated by hyphens: 550e8400-e29b-41d4-a716-446655440000.

UUIDs solve a fundamental problem in distributed systems: how do you assign unique identifiers without a central authority? Auto-increment IDs require a single database to coordinate. UUIDs can be generated independently on any machine, at any time, with virtually zero collision risk.

UUID Versions Explained

• v1 — Based on timestamp + MAC address. Unique but reveals when and where it was generated. Privacy concern.
• v4 — Random. 122 random bits. This is the most widely used version and what our tool generates. No information leakage.
• v5 — Namespace-based using SHA-1. Deterministic — same input always produces the same UUID. Useful for creating consistent IDs from known values.
• v7 (2024) — Timestamp-sortable random UUID. New standard gaining adoption for database primary keys because they are both unique and chronologically sortable.

When to Use UUIDs

• Database primary keys. When you need IDs that can be generated client-side, across multiple servers, or before inserting into the database.
• API resource identifiers. UUIDs in API URLs (e.g., /users/550e8400-e29b-41d4-a716-446655440000) don't reveal record count or creation order.
• Distributed systems. Microservices generating IDs independently without coordinating with a central database.
• Session tokens. Random UUIDs make unpredictable session identifiers (though dedicated session management is better for production).
• Test data. Generating realistic-looking unique IDs for development and testing environments.
• File naming. Unique filenames for uploads, exports, and temporary files.

UUID vs. Auto-Increment IDs

Feature	UUID v4	Auto-Increment
Uniqueness scope	Global	Per-table
Generation	Anywhere, anytime	Database only
Predictability	Random (secure)	Sequential (guessable)
Storage size	16 bytes	4-8 bytes
Index performance	Slower (random order)	Faster (sequential)
Information leakage	None	Reveals record count

Rule of thumb: Use auto-increment for simple applications with a single database. Use UUIDs for distributed systems, public-facing APIs, or any context where predictable IDs are a security concern.

UUID Format and Structure

A v4 UUID looks like: xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx where each x is a random hex digit, the 4 indicates version 4, and y is one of 8, 9, A, or B (indicating the variant).

Total: 32 hex digits, 4 hyphens, 36 characters. The hyphens are cosmetic — they can be stripped for storage and added back for display.

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Frequently Asked Questions

Are UUIDs truly unique?

Practically, yes. A v4 UUID has 122 random bits, creating 5.3 × 10^36 possible values. The probability of collision is astronomically low — you would need to generate 2.71 × 10^18 UUIDs to have a 50% chance of one duplicate. In practice, you will never generate a duplicate UUID.

Are the generated UUIDs cryptographically secure?

Yes. The generator uses crypto.getRandomValues(), which is a cryptographically secure pseudorandom number generator (CSPRNG) built into all modern browsers. This is the same random source used for generating encryption keys.

Can I generate UUIDs in bulk?

Yes. The tool supports bulk generation — generate as many UUIDs as you need and copy them all at once. Useful for seeding databases, creating test data, or pre-generating IDs.

Should I use UUIDs as database primary keys?

It depends. UUIDs are excellent for distributed systems and public APIs. The tradeoff is slightly larger storage (16 bytes vs. 4-8 bytes) and slower index performance due to randomness. For most applications, the tradeoff is worth the benefits.

What is the difference between UUID and GUID?

They are the same thing. UUID is the standard term (RFC 4122). GUID (Globally Unique Identifier) is Microsoft terminology. The format and generation are identical.