Example
Options
Version: UUID v7 Count: 3 Uppercase: off
Output (UUID v7 · 3 ids)
0192f5a4-b6e0-7c1e-9d4f-1a2b3c4d5e6f 0192f5a4-b6e1-7203-8a9b-cd1234ef5678 0192f5a4-b6e2-7c01-b1c2-aabbccddeeff
Note
v7's leading 48 bits are an ms timestamp, so IDs sort chronologically. Within the same millisecond the trailing random bits differ — collision probability is effectively zero.
Usage / FAQ
When to use
- Generate unique identifiers for database primary keys
- Get collision-free IDs across distributed systems (UUID v4)
- Time-ordered IDs for better DB index locality (UUID v7 / ULID)
- Fill mock test data with realistic ID fields
- Random session tokens with effectively zero collision probability
FAQ
- Q.UUID v4 vs v7?
- A.v4 is 122-bit fully random — most common but poor DB index locality. v7 (RFC 9562, 2024) uses 48-bit ms timestamp + random — time-ordered, index-friendly.
- Q.What's ULID?
- A.ULID is Crockford Base32, 26 chars — more human-readable, also time-sortable. Shorter and URL-safe than UUID.
- Q.Which one should I use?
- A.For new DB primary keys, UUID v7 or ULID recommended. For external API compatibility, v4 stays the safe default. For human-facing trace IDs, ULID's compactness wins.
Fun facts
UUID v4 has 2¹²² ≈ 5.3 × 10³⁶ possible values. Generating one billion per second, you would need roughly 85 billion years before there's a 50% chance of any two colliding — about six times the age of the universe (13.8 billion years). That's where "practically impossible to collide" comes from.
Wikipedia — UUID collisionsUUIDs trace back to Apollo Computer's NCS (Network Computing System) in the 1980s. The goal: make collision-free IDs in distributed systems without any central authority. That work eventually became DCE and was standardized as RFC 4122 in 2005.
RFC 4122UUID v7 was formalized as RFC 9562 in May 2024. v4 is fully random — terrible for DB index locality. v7 uses a 48-bit millisecond timestamp prefix, giving you time-ordering AND index friendliness in the same value. For new systems, v7 is the recommended default.
RFC 9562 (2024)
Related guides
- UUID vs ULID — Which Identifier Should You Use?
UUID v4, UUID v7, ULID, and Snowflake compared on sortability, database performance, URL friendliness, and collision risk.
- Web Crypto API — SHA, HMAC, AES, and JWT in the Browser Without Libraries
Native crypto.subtle in browsers — digest, sign/verify, encrypt/decrypt, key import/export, and why getRandomValues replaces Math.random for security.
- Idempotency Keys — How Stripe Makes Retries Safe and How to Implement Them
Why retries cause duplicate charges, how Stripe and PayPal use idempotency keys, the server-side state machine, key generation strategies, and storage TTL.
- Rate Limiting Strategies — Token Bucket, Sliding Window, and the 429 Retry-After Contract
Why rate limit, the four classic algorithms (fixed window, sliding window, token bucket, leaky bucket), how to scope by IP/user/API key, and the headers clients expect.
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