UUID Generator - Generate Random UUIDs (v4) Online

How This Tool Works

Our UUID generator creates version 4 UUIDs using the browser's crypto.randomUUID() method when available, or falls back to crypto.getRandomValues() for older browsers. Both methods tap into your operating system's cryptographically secure random number generator (CSPRNG), the same source used for SSL/TLS encryption. This ensures the generated UUIDs are truly random, not based on predictable pseudo-random algorithms.

A UUID v4 consists of 128 bits (16 bytes) of data displayed as 32 hexadecimal characters divided into five groups by hyphens: 8-4-4-4-12. The '4' in the third group indicates version 4, and specific bits in the fourth group are set to identify the variant. With 122 bits of randomness (6 bits are fixed for version and variant), UUID v4 provides approximately 5.3×10³⁶ possible combinations—more than the number of atoms in a human body.

The tool generates UUIDs entirely in your browser's memory with zero network communication. You can create thousands instantly, format them according to your needs (with/without hyphens, with braces, uppercase), and download them as text files for bulk use in databases, APIs, or configuration files.

Why Use This Tool

While UUIDs can be generated through programming languages and command-line tools, our web-based generator provides immediate access without technical setup:

• No development environment needed: Generate UUIDs instantly without opening an IDE, installing libraries, or writing code—perfect for non-developers or quick tasks
• Bulk generation: Create hundreds of UUIDs at once for database seeding, testing, or migrations—much faster than running scripts repeatedly
• Format flexibility: Switch between standard, compact, braced, or uppercase formats instantly without string manipulation code
• Cross-platform accessibility: Works on any device with a browser—generate UUIDs on your phone, tablet, or computer without OS-specific tools
• Educational value: See UUID format and statistics in real-time, helping understand the structure and collision probability

Compared to online UUID generators that show ads or limit generation, ours is completely free with no restrictions. Compared to command-line tools like uuidgen, it provides a friendlier interface with visual feedback and easy copying to clipboard.

UUID Generator Tool

Generate cryptographically strong universally unique identifiers (UUIDs) instantly. Our free UUID generator creates version 4 UUIDs using secure random number generation, perfect for database keys, session tokens, and distributed systems.

How to Generate UUIDs

1. Select Quantity: Enter the number of UUIDs you need (1-1000).
2. Choose Format: Select your preferred format (standard, compact, with braces, or uppercase).
3. Add Version Label: Optionally include the version identifier.
4. Generate: Click "Generate UUID(s)" or "Generate 100 UUIDs" for bulk creation.
5. Copy or Download: Use the buttons to copy to clipboard or download as a text file.

UUID Format Explained

A standard UUID v4 follows this format: xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx

• x: Any hexadecimal digit (0-9, a-f)
• 4: Version indicator (always 4 for UUID v4)
• y: One of 8, 9, a, or b (variant bits)
• Total length: 36 characters including hyphens, 32 without

Common UUID Use Cases

UUIDs are essential in modern software development:

• Database Primary Keys: Unique identifiers for database records
• Distributed Systems: IDs that don't require central coordination
• Session Management: Unique session identifiers for web applications
• File Naming: Ensure unique file names in storage systems
• Transaction IDs: Track individual transactions across systems
• Message Queuing: Unique message identifiers in queuing systems
• API Requests: Request tracing and idempotency keys
• Resource Identifiers: Unique IDs for resources in RESTful APIs

UUID Versions Comparison

Different UUID versions serve different purposes:

• Version 1: Time-based with MAC address. Predictable but reveals system info.
• Version 3: MD5 hash-based, namespace-derived. Deterministic.
• Version 4: Random generation. Most common, no system info exposure.
• Version 5: SHA-1 hash-based, namespace-derived. More secure than v3.

Advantages of UUID v4

Why UUID v4 is the most popular choice:

• No Coordination Needed: Generate IDs independently across systems
• Privacy: Doesn't expose MAC addresses or timestamps
• Simplicity: Easy to generate without additional context
• Collision Resistance: Practically impossible to generate duplicates
• Portability: Works across different platforms and languages
• No Central Registry: No need for centralized ID generation service

Best Practices

Follow these guidelines when using UUIDs:

• Use for Distribution: Ideal when multiple systems generate IDs independently
• Consider Storage: UUIDs use more storage than integers (16 bytes vs 4-8 bytes)
• Index Performance: Random UUIDs can impact B-tree index performance
• Not for Security: Don't use as security tokens; they're predictable in sequence
• Version Choice: Use v4 for general use, v5 for deterministic requirements
• Case Sensitivity: Treat UUIDs as case-insensitive

UUID in Different Programming Languages

Generate UUIDs in popular languages:

• JavaScript: crypto.randomUUID() or uuid library
• Python: uuid.uuid4() from uuid module
• Java: UUID.randomUUID() from java.util.UUID
• C#: Guid.NewGuid() from System namespace
• PHP: uniqid() or ramsey/uuid library
• Ruby: SecureRandom.uuid
• Go: uuid.New() from github.com/google/uuid

Database Considerations

When using UUIDs as database primary keys:

• Storage Type: Use native UUID type when available (PostgreSQL, MySQL 8+)
• Indexing: Consider ordered UUIDs (like UUIDv7) for better B-tree performance
• Display: Store as binary, display as string for efficiency
• Foreign Keys: Consistent UUID usage across related tables
• Clustering: Be aware of potential index fragmentation with random UUIDs

Performance Considerations

Understanding UUID performance implications:

• Generation Speed: v4 is fast, no external dependencies needed
• Storage Size: 128 bits (16 bytes) vs 64 bits (8 bytes) for BIGINT
• Index Performance: Random nature can cause index fragmentation
• Comparison Speed: Slower than integer comparison
• Memory Usage: More memory per record in applications

Alternatives to UUIDs

When UUIDs might not be the best choice:

• Auto-increment IDs: For single-database systems without distribution needs
• Snowflake IDs: Time-ordered, k-sortable, more compact
• ULID: Lexicographically sortable, timestamp-based
• KSUID: Time-ordered, more human-readable than UUIDs
• NanoID: Shorter, URL-friendly, configurable length

Security Notes

Important security considerations:

• UUIDs are NOT cryptographically secure tokens
• Don't use UUIDs for password reset tokens or authentication
• UUIDs can be guessed in sequence by observing patterns
• For security tokens, use cryptographically secure random generators
• Consider HMAC or JWT for authenticated tokens

Limitations & Things to Know

While UUIDs are extremely reliable, understanding these points ensures proper usage:

• Not truly "unique" but practically unique: UUID v4 collision probability is astronomically low (~1 in 5.3×10³⁶), but mathematically possible. For absolute uniqueness guarantees, consider UUID v1 or sequential IDs.
• Not suitable for security tokens: UUIDs are identifiers, not secrets. Don't use them as passwords, API keys, or authentication tokens—they lack sufficient entropy and security properties for those purposes.
• Storage overhead: UUIDs consume 16 bytes as binary or 36 characters as text, significantly more than integer IDs (4-8 bytes). This matters at scale—a billion records means 16GB+ just for IDs.
• Database index performance: Random UUID v4 values cause B-tree index fragmentation in databases, potentially slowing inserts. Consider sequential UUIDs (UUID v7) or clustering strategies for high-traffic systems.
• Not sortable by time: UUID v4 is completely random with no timestamp component. If you need time-ordered IDs, use UUID v1, v6, or v7, or consider alternatives like ULIDs or Snowflake IDs.
• Browser requirement: Requires modern browsers with Web Crypto API (2017+). Ancient browsers may fail to generate secure UUIDs.
• No persistence: Generated UUIDs aren't saved. If you close the page, you must regenerate. For production use, generate UUIDs at the point of use in your application.
• Format compatibility: Some systems expect UUIDs with hyphens, others without. Some want uppercase, others lowercase. Always check your system's requirements before bulk generation.