Developer Tool

UUID / GUID Generator

Generate UUID v1, v4, and v5 identifiers instantly — one at a time or in bulk up to 1,000. Multiple formats supported. Everything runs in your browser, zero server calls.

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UUID v4 — Generated from cryptographically secure random bytes. The most widely used version. Ideal for primary keys, session tokens, and any context where global uniqueness is needed without coordination between systems.
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What Is a UUID and When Should You Use One?

UUID vs. Auto-Increment IDs

Sequential integers (1, 2, 3…) are simple but expose information: a user with ID 1042 knows roughly how many accounts exist. They're also impossible to merge across databases without collision. UUIDs solve both problems — they're globally unique by design, generated independently on any machine without coordination, and reveal nothing about the size or sequence of your dataset.

UUID v4 vs. v1: Which to Use?

UUID v4 is the right default for most use cases. It's 122 bits of random data with no embedded system information. UUID v1 encodes a timestamp and the generating machine's MAC address, making it sortable chronologically — useful for time-ordered event logs. However, v1 exposes hardware identifiers, which can be a privacy concern in user-facing contexts. When in doubt, use v4.

Deterministic UUIDs with v5

UUID v5 generates the same UUID every time for the same namespace and name combination. This makes it ideal for content-addressable systems: if you want a stable, unique ID for a URL, a file path, or a user email without storing a lookup table, v5 gives you that. Run the same inputs tomorrow and get the same UUID. Common namespaces like DNS and URL are standardised in RFC 4122.

Common Developer Use Cases

  • Database primary keys — Distribute record creation across microservices without ID conflicts.
  • Session and request tokens — Unpredictable, collision-resistant identifiers for user sessions.
  • File and asset naming — Upload files with UUID names to prevent overwrites and enumeration.
  • Idempotency keys — Attach a UUID to API requests to safely retry without duplicating operations.
  • Event tracking — Assign permanent IDs to analytics events before they're written to a database.

Frequently Asked Questions

UUID v4 contains 122 bits of randomness, meaning there are 2¹²² ≈ 5.3 × 10³⁶ possible values. To have a 50% chance of generating even a single collision, you would need to generate roughly 2.7 × 10¹⁸ UUIDs — that's 2.7 quintillion. At a rate of one billion UUIDs per second, it would take about 86 years to reach that threshold. For any practical system, UUID v4 collisions are statistically impossible.
Functionally, they are the same thing. GUID (Globally Unique Identifier) is Microsoft's term for its implementation of the UUID standard, used throughout the Windows API, COM, and .NET. UUID (Universally Unique Identifier) is the term used in the RFC 4122 standard and in most open-source ecosystems. Both follow the same 8-4-4-4-12 hexadecimal format and are fully interchangeable.
Yes. v4 UUIDs are generated using crypto.getRandomValues() from the Web Crypto API, which is the same cryptographically secure random number generator used in production UUID libraries. v5 UUIDs use crypto.subtle.digest for SHA-1 hashing. Both are browser-native, well-tested primitives that meet RFC 4122 requirements.
Yes, and it's a common pattern in distributed systems. The main trade-off versus sequential integer keys is index fragmentation: because UUIDs are random, new rows are inserted into random positions in a B-tree index rather than always at the end. This can reduce insert performance on very large tables. Solutions include using UUID v7 (time-ordered, not yet widely supported), storing UUIDs as binary(16) instead of varchar(36), or using database-specific ordered UUID strategies.
The URN (Uniform Resource Name) format prefixes the UUID with urn:uuid:, producing a string like urn:uuid:550e8400-e29b-41d4-a716-446655440000. This is the formal RFC representation and is used in XML schemas, SAML assertions, and contexts where the identifier needs to be an unambiguous URI. For most web applications and databases, the standard hyphenated format without the prefix is sufficient.