UUID Generator

A UUID — universally unique identifier — is a 128-bit value you can generate anywhere, on any machine, without checking whether anyone else has used it. That single property makes distributed systems, offline apps and data merges dramatically simpler.

How it works

• 128 random bits are drawn from crypto.randomUUID(), the browser's secure generator.
• Four bits are set to mark it as version 4, and two more mark the RFC 4122 variant.
• The remaining 122 bits stay random.
• The result is written as 8-4-4-4-12 hexadecimal digits.

A worked example

In 3f2b9c4e-7a1d-4f8e-9b2c-5d6e7f8a9b0c, the 4 starting the third group identifies it as version 4, and the 9 starting the fourth group marks the variant. Every other digit is random. That's why you can spot a v4 UUID at a glance — the 13th character is always 4.

How to interpret your result

All the identifiers here are equally valid and equally unique. Choose hyphens for the canonical form used in APIs and documentation; strip them when a system requires a compact 32-character string. Store one format consistently rather than mixing.

Common real-world uses

• Primary keys for records created across multiple services or devices.
• Correlation IDs for tracing a request through distributed logs.
• Idempotency keys so a retried payment doesn't charge twice.
• Unique file names for uploads that must never overwrite each other.
• Test fixtures and seed data that need guaranteed-distinct values.

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