UUID (Universally Unique Identifier) is a 128-bit identifier guaranteed to be unique across space and time without central coordination. Format: 8-4-4-4-12 hexadecimal digits (e.g., 550e8400-e29b-41d4-a716-446655440000). UUIDs are used as database primary keys, session IDs, file names, and distributed system identifiers. The probability of collision is negligible: generating 1 billion UUIDs per second for 100 years yields < 50% collision chance.

What is the difference between UUID v4 and other versions?

UUID v1 uses timestamp + MAC address (leaks machine info, not recommended). UUID v4 uses random numbers (most common, no privacy concerns). UUID v5/v3 use hashing (deterministic, same input = same UUID). UUID v7 (new) uses timestamp + random (sortable, time-ordered). For general use, v4 is recommended: fully random, no collisions, no privacy leaks. v7 is preferred for database primary keys requiring chronological ordering.

Can two UUID v4s ever be the same?

Theoretically yes, but astronomically unlikely. With 122 random bits (6 bits reserved for version/variant), there are 2^122 possible UUIDs (5.3 undecillion). Generating 1 trillion UUIDs gives a 0.00000000006% collision chance. In practice, collision is impossible for human-scale systems. For absolute certainty, use UUID v5 with namespace control or database unique constraints.

Are UUIDs secure for authentication tokens?

No. While UUIDs are unpredictable, they are not cryptographically secure. UUIDs use 122 random bits; secure tokens require 128-256 bits of cryptographic randomness. For session tokens, API keys, or password reset tokens, use cryptographically secure random generators (crypto.randomBytes() in Node.js, secrets module in Python). UUIDs are perfect for non-security identifiers: database IDs, file names, correlation IDs.

How do I use UUIDs in databases?

Most databases support UUID types: PostgreSQL (UUID column type), MySQL (CHAR(36) or BINARY(16)), MongoDB (Binary subtype 4). Store UUIDs as binary (16 bytes) for efficiency; convert to string (36 chars) only for display. Trade-offs: UUIDs avoid auto-increment contention in distributed systems but are larger than integers and reduce index performance. For high-performance single-server databases, consider auto-increment integers; for distributed systems, use UUIDs.

Can I use UUIDs as file names?

Yes. UUIDs make excellent file names because they are unique, filesystem-safe (no special characters), and avoid naming conflicts. Example: "550e8400-e29b-41d4-a716-446655440000.jpg". This is common for user uploads, temporary files, and cloud storage (S3, GCS). However, UUIDs are not human-readable; consider including metadata: "profile_550e8400.jpg" or using UUIDs as directory names with descriptive file names inside.

UUID Generator - Generate v4 UUIDs Online

How to Generate UUIDs

Enter number of UUIDs to generate (1-100)
Click generate
View unique UUIDs (v4 format)
Copy individual or all UUIDs

UUID Generator Features

UUID v4 Generation: Random 128-bit identifiers
Batch Generation: Create 1-100 UUIDs at once
Cryptographically Secure: Uses secure random number generation
Copy Individual or All: Flexible copying options
Standard Format: Lowercase with hyphens (8-4-4-4-12)
100% Free: No limits on generation

What are UUIDs?

UUIDs (Universally Unique Identifiers) are 128-bit values guaranteed to be unique. UUIDv4 uses random generation with 2^122 possible combinations. Format: 8-4-4-4-12 hexadecimal digits. Chance of collision is negligible (1 in 5.3 undecillion).

Example UUID: c9bf9e57-1685-4c89-bafb-ff5af830be8a. The third group always starts with 4 (indicating version 4), and the fourth group starts with 8, 9, a, or b (indicating variant). These constraints ensure standard compliance while maintaining randomness.

Use cases: Database primary keys without auto-increment, API request IDs for tracking, session identifiers for web applications, file naming to prevent conflicts, distributed system identifiers, and tracking unique events in analytics.

Privacy & Security

All UUID generation happens locally in your browser using cryptographically secure random numbers. No UUIDs are uploaded to servers, stored, or logged. The generation uses JavaScript, keeping your identifiers completely private.

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