UUID stands for Universally Unique Identifier . It's a 128-bit label defined by RFC 4122 (and updated by RFC 9562) used to uniquely identify information in computer systems without a central authority. UUIDs are commonly used as primary keys in databases, identifiers in APIs, and correlation IDs in logging.

What makes UUID v4 different from other versions?

UUID v4 is randomly generated — 122 of its 128 bits come from a cryptographically secure random source ( crypto.randomUUID() ). Other versions use different strategies: v1 encodes a timestamp + MAC address, v3 and v5 use MD5/SHA-1 hashes of a namespace + name, and v7 (newer) uses a Unix timestamp prefix for sortability. For most use cases where you just need a unique ID without ordering requirements, v4 is the simplest and most common choice.

Are UUID v4 values safe to use as database primary keys?

Yes. The collision probability is astronomically low — approximately 1 in 5.3 × 10³⁶ for any two given UUIDs. In practice, you would need to generate about 2.7 × 10¹⁸ UUIDs before the probability of a single collision exceeds 50%. Note that UUID v4's random ordering can cause index fragmentation in B-tree databases at very high insert rates; if that's a concern, consider UUID v7 which is time-ordered.

Does this tool send my UUIDs to a server?

No. Everything is generated entirely in your browser using the built-in crypto.randomUUID() Web API. No data is sent to any server. You can even disconnect from the internet and the tool will continue to work.

UUID Generator — Free Online Tool

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Single UUID

단일 UUID

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About UUID v4

UUID v4 정보

UUID v4 (Universally Unique Identifier version 4) is defined by RFC 4122. Each UUID is 128 bits — represented as 32 hexadecimal digits in the format xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx. The 4 at position 13 identifies the version, and the variant bits at position 17 are set to 8, 9, a, or b. The remaining 122 bits are randomly generated using the browser's crypto.randomUUID(), which uses a cryptographically secure pseudo-random number generator (CSPRNG). The probability of two v4 UUIDs colliding is astronomically small — roughly 1 in 5.3 × 10³⁶.

UUID v4(Universally Unique Identifier version 4)는 RFC 4122 표준에 정의되어 있습니다. 각 UUID는 128비트이며 xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx 형식의 32자리 16진수로 표현됩니다. 13번째 자리의 4가 버전을 나타내고, 17번째 자리에 배리언트 비트(8, 9, a, b 중 하나)가 설정됩니다. 나머지 122비트는 무작위로 생성되며, 브라우저의 crypto.randomUUID()가 암호학적으로 안전한 난수 생성기(CSPRNG)를 사용합니다. 두 UUID가 충돌할 확률은 약 5.3 × 10³⁶ 분의 1로 사실상 불가능합니다.

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