Generate random UUID v4 identifiers online. Create unique 128-bit identifiers for databases, APIs, and software development instantly.
A UUID (Universally Unique Identifier) is a 128-bit label used to uniquely identify information in computer systems without requiring a central registration authority. The version 4 UUID is generated using random or pseudo-random numbers, making it the most widely used variant in modern software development.
Our free online UUID Generator instantly creates valid v4 UUIDs in the standard 8-4-4-4-12 hexadecimal format. Whether you need identifiers for database primary keys, API request tracing, session tokens, or distributed-system message IDs, this tool delivers cryptographically random UUIDs ready to copy and paste.
UUIDs are essential in microservices architectures, event-driven systems, and any application that must produce unique identifiers without database round-trips. With approximately 5.3 × 10³⁶ possible v4 UUIDs, the probability of a collision is astronomically low, making them safe for virtually every use case.
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Generating UUIDs by hand or looking up online services interrupts your development flow. This generator produces valid v4 UUIDs in one click, directly in your browser, with no server requests and no data stored anywhere. Use it whenever you need a quick unique ID for testing, prototyping, or configuration files.
A v4 UUID follows the pattern: xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx, where x is any hexadecimal digit and y is one of 8, 9, a, or b. The "4" in the third group indicates version 4 (random). The variant bits in the fourth group restrict y to {8, 9, a, b}.
Result: 550e8400-e29b-41d4-a716-446655440000
The generator produces a 128-bit identifier formatted as five groups of hexadecimal digits separated by hyphens. The third group always starts with 4 (version), and the fourth group's first digit is 8, 9, a, or b (variant). Every generation yields a new unique value.
The UUID specification (RFC 4122 and its successor RFC 9562) defines several versions. Version 1 concatenates a timestamp with the generating machine's MAC address, offering rough time ordering but leaking hardware identity. Versions 3 and 5 hash a namespace and name with MD5 and SHA-1, producing deterministic identifiers.
Version 4 replaces all fields (except version and variant markers) with random bits, making it the simplest and most privacy-friendly variant. The newer version 7 (RFC 9562) embeds a Unix millisecond timestamp while keeping random trailing bits, combining time-sortability with uniqueness.
When storing UUIDs in relational databases, convert them to binary(16) to save storage and improve index performance. Many databases—PostgreSQL, MySQL 8+, SQL Server—offer native UUID column types.
In API design, UUIDs make excellent resource identifiers because they expose no information about creation order or volume. This prevents enumeration attacks and simplifies merging data from multiple sources.
A version 4 UUID is a 128-bit identifier generated from random or pseudo-random numbers. It follows the format xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx and is defined by RFC 4122. The "4" marks the version, and the variant bits restrict certain positions.
While not guaranteed unique, the probability of generating a duplicate v4 UUID is negligibly small—roughly 1 in 2¹²² possibilities. You would need to generate about 2.71 quintillion UUIDs to have a 50% chance of a single collision.
GUID (Globally Unique Identifier) is Microsoft's term for the same concept. GUIDs and UUIDs are functionally identical 128-bit identifiers. The terms are used interchangeably in most contexts.
Yes. UUIDs work well as primary keys in distributed systems because they can be generated on any node without coordination. The trade-off is that random UUIDs can cause index fragmentation in B-tree indexes; consider UUID v7 for ordered inserts.
This tool uses Math.random() which is not cryptographically secure in all browsers. For security-sensitive tokens (session IDs, API keys), use crypto.randomUUID() or a server-side cryptographic library instead.
A standard UUID string contains 36 characters: 32 hexadecimal digits plus 4 hyphens, grouped as 8-4-4-4-12. The underlying value is 128 bits or 16 bytes.
UUID v1 uses timestamp and MAC address; v3 and v5 are namespace-based using MD5 and SHA-1 respectively; v4 is fully random; v6 and v7 (newer) are time-sortable variants. V4 and v7 are the most popular for modern applications.