UUIDジェネレーター
ランダムなUUID/GUID識別子を生成
関連ツール
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UUIDs: Universally Unique Identifiers Explained
Key Takeaways
- UUIDs (v4) use 122 bits of randomness to generate identifiers that are statistically guaranteed to be unique across all systems worldwide.
- UUID v4 is the most common version — purely random with no embedded timestamp or machine information.
- All UUIDs are generated in your browser using cryptographic randomness — nothing is stored or transmitted.
Universally Unique Identifiers (UUIDs) solve the fundamental distributed systems problem of generating unique identifiers without central coordination. Whether you are building microservices, designing database schemas, or creating distributed systems, UUIDs provide a standardized way to create identifiers that will never collide, even across independent systems.
The probability of generating two identical UUID v4 values is approximately 1 in 5.3 x 10^36.
Collision Probability
Key Concepts
UUID Versions
UUID v1 uses timestamp + MAC address. V3 uses MD5 namespace hashing. V4 uses pure randomness. V5 uses SHA-1 namespace hashing. V7 (new) combines timestamp with randomness for sortability.
UUID v4 Structure
A UUID v4 follows the format xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx where '4' indicates version 4 and 'y' is constrained to 8, 9, a, or b to indicate the variant. The remaining 122 bits are random.
UUID vs. Auto-Increment IDs
Auto-increment IDs are sequential and predictable, leaking information about record count and creation order. UUIDs are random and reveal nothing, making them better for public-facing identifiers.
UUID v7 — The New Standard
UUID v7 (RFC 9562) embeds a Unix timestamp in the first 48 bits, making UUIDs naturally sortable by creation time while maintaining randomness. This is ideal for database primary keys.
Pro Tips
Use UUID v7 for database primary keys — the embedded timestamp makes them naturally sortable, improving B-tree index performance.
Store UUIDs as binary (16 bytes) in databases rather than as strings (36 characters) for significant storage and performance gains.
Remove hyphens when UUIDs are used in URLs to keep them compact while maintaining readability.
Use crypto.randomUUID() in modern browsers — it is faster and more secure than JavaScript UUID libraries.
All UUIDs are generated entirely in your browser using the Web Crypto API. No generated identifiers are stored, logged, or transmitted to any server.