What is a UUID and why should I use one?

A UUID (Universally Unique Identifier) is a 128-bit number used to uniquely identify information in computer systems. UUIDs are practically guaranteed to be unique across all devices and time—the probability of collision is astronomically low. Use UUIDs for database primary keys where auto-incrementing integers aren't suitable, unique session identifiers for user tracking, API tokens and request IDs for distributed systems, file names to avoid naming conflicts, and transaction IDs in financial systems. UUIDs eliminate coordination requirements between systems—you can generate IDs independently without checking a central authority. They're standardized by RFC 4122 and supported by virtually all programming languages and databases.

What's the difference between UUID v1, v4, and v5?

UUID v1 combines timestamp, clock sequence, and MAC address to guarantee uniqueness. It's time-sortable but can reveal the generating machine's MAC address and creation time. UUID v4 uses random or pseudo-random numbers for the entire 122 bits (6 bits are reserved for version/variant). It's the most common version, offers strong randomness, and reveals no information about when or where it was created. UUID v5 uses SHA-1 hashing of a namespace identifier and a name. It's deterministic—the same namespace and name always produce the same UUID, making it reproducible and useful for generating consistent IDs from known inputs. For most applications, use v4 for simplicity and privacy. Use v1 when time-based sorting matters. Use v5 when you need deterministic, reproducible UUIDs.

How do I generate multiple UUIDs at once (bulk generation)?

Most UUID generators include a bulk generation feature where you specify the number of UUIDs needed and the tool generates them all at once. Look for a quantity input field or bulk generation option—you can typically generate anywhere from 1 to 10,000+ UUIDs in a single operation. The generated UUIDs appear in a list format, ready to copy individually or all at once. This is invaluable when seeding databases with test data, generating API keys for multiple clients, creating unique identifiers for batch processing, or preparing IDs for import into other systems. Bulk generation happens instantly in your browser without server requests, ensuring privacy and speed.

Are UUIDs truly unique? What's the collision probability?

UUIDs are practically unique, though not mathematically guaranteed. For UUID v4 (random), with 122 random bits, the probability of collision is approximately 1 in 2^122 (about 5.3 x 10^36). To put this in perspective, generating 1 billion UUIDs per second would take over 100 years before reaching a 50% probability of a single collision. For UUID v1, uniqueness is guaranteed as long as the MAC address is unique and you don't generate more than 10,000 UUIDs in a 100-nanosecond interval on the same machine. In practice, UUID collisions are so rare that they're not a concern for most applications. Systems would fail from hardware errors long before UUID collisions become statistically significant.

Can I validate or decode existing UUIDs?

Yes! UUID validators check if a string conforms to the UUID format: 8-4-4-4-12 hexadecimal characters (like 550e8400-e29b-41d4-a716-446655440000). Validators ensure proper length, character types, version bits, and variant bits. UUID decoders extract information from UUIDs—for v1, they can reveal the timestamp and MAC address; for v4, they confirm randomness; for v5, they show the hashing algorithm. Decoding helps debug UUID generation issues, verify UUID versions, and understand UUID origins. Most tools accept UUIDs with or without hyphens. If validation fails, check for typos, missing characters, or incorrect formatting.

Should I use UUIDs or auto-incrementing integers for database primary keys?

It depends on your use case. Use UUIDs when you need distributed ID generation (multiple servers creating records simultaneously), want to merge databases without ID conflicts, need to generate IDs client-side before server insertion, require non-sequential IDs for security (prevent enumeration attacks), or plan to shard/partition your database in the future. Use auto-incrementing integers when database performance is critical (UUIDs are larger and slower to index), you need human-readable sequential IDs, storage space is limited (UUIDs use 16 bytes vs 4-8 for integers), or your database will remain centralized and small. Many modern applications use UUIDs for flexibility despite the slight performance trade-off. PostgreSQL's UUID type and MySQL's UUID functions make them first-class citizens.

How do I use generated UUIDs in my code or database?

After generating UUIDs with this tool, copy them and paste into your code or database. In SQL databases, use UUID or CHAR types (depending on database). PostgreSQL has a native UUID type. MySQL uses CHAR(36) or binary UUID functions. In programming languages, most have built-in UUID support—JavaScript has crypto.randomUUID(), Python has uuid module, Java has java.util.UUID, and C# has System.Guid. For API development, use UUIDs as resource identifiers in URLs and request/response bodies. Store UUIDs as strings in JSON, binary in databases for efficiency, or lowercase hexadecimal without hyphens for maximum compatibility. Always validate UUID format when accepting from external sources to prevent injection attacks or data corruption.

Can I customize or namespace UUIDs for different purposes?

UUID v5 supports namespacing through the namespace identifier parameter. Standard namespaces exist for DNS (domain names), URLs, OIDs (object identifiers), and X.500 distinguished names. You can also create custom namespaces by generating a UUID v4 and using it as a namespace for v5 UUIDs. For example, create a namespace UUID for 'users' and another for 'orders', then generate v5 UUIDs within each namespace using usernames or order numbers as the name parameter. This ensures consistent UUIDs for the same input while preventing collisions across different entity types. UUID v1 and v4 don't support namespacing—they're always globally unique regardless of context.

Is it safe to expose UUIDs publicly in URLs or APIs?

Generally yes, especially UUID v4 which is random and reveals no information about your system. Unlike auto-incrementing integers (which expose record count and allow enumeration), UUIDs are unpredictable and don't leak business intelligence. However, consider these factors: UUID v1 exposes MAC address and timestamp, potentially revealing infrastructure details—avoid in public APIs. Even with UUIDs, implement proper authorization checks—obscurity isn't security. Don't rely solely on UUID secrecy for access control. For public APIs, v4 is ideal because it's random, non-sequential, and reveals nothing. For extremely sensitive resources, consider additional security measures like signed URLs or time-limited tokens alongside UUIDs.

Why are UUIDs represented with hyphens (8-4-4-4-12 format)?

The hyphenated format (like 550e8400-e29b-41d4-a716-446655440000) improves readability by visually separating the UUID's logical components. The format reflects the UUID's internal structure: first 8 characters (time-low or random), next 4 (time-mid or random), next 4 (time-high-and-version or random), next 4 (clock-seq-and-reserved or random), and last 12 (node or random). Hyphens make UUIDs easier to read, compare, and debug. However, storage and comparison are more efficient without hyphens—many systems store UUIDs as 32 hexadecimal characters or 16-byte binary. Most UUID tools and libraries accept both formats. Some databases automatically convert between formats. When sharing UUIDs with humans, use hyphens. When optimizing for storage or performance, omit them.

Free UUID Generator

Generate UUIDs (Universally Unique Identifiers) online for free. Support for UUID v1, v4, v5, bulk generation, validation, and decoding. Perfect for database keys, session IDs, and API tokens.

Generator Settings

Configure UUID generation options

UUID Version

UUID v4 (Random)

Random UUID - most commonly used

UUID v1 (Time-based)

Based on timestamp and MAC address

UUID v3 (MD5)

Based on namespace and name using MD5

UUID v5 (SHA-1)

Based on namespace and name using SHA-1

Nil UUID

All zeros - 00000000-0000-0000-0000-000000000000

Number of UUIDs: 1

1100

Generated UUIDs

No UUIDs generated yet

Click "Generate UUIDs" to create your first UUID

UUID Information

UUID Versions

v1: Time-based with MAC address
v3: Name-based using MD5 hashing
v4: Random or pseudo-random
v5: Name-based using SHA-1 hashing
Nil: Special case of all zeros

Common Use Cases

• Database primary keys
• API request/response IDs
• File names and identifiers
• Session tokens
• Distributed system IDs

UUID Generator FAQ - Common Questions

Find answers to frequently asked questions about UUIDs, UUID versions (v1, v4, v5), generation, validation, use cases, and best practices for using UUIDs in your applications.

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