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About This Tool
RFC 9562 defines UUID Version 7 as a modern, timestamp-ordered replacement for random UUIDv4 and sequential auto-incrementing integer IDs. By placing a 48-bit Unix epoch millisecond timestamp at the beginning of the 128-bit structure, UUIDv7 preserves chronological sortability, eliminates database B-Tree index page-splitting, and retains cryptographic uniqueness across distributed nodes.
### Anatomy of an RFC 9562 UUIDv7 Identifier
A UUIDv7 string follows standard 8-4-4-4-12 hyphenation while organizing bit fields into structured time and entropy components: - **Unix Timestamp (48 bits):** The first 36 hex characters encode milliseconds elapsed since Unix epoch (`1970-01-01T00:00:00Z`), ensuring natural chronological ordering. - **Version (4 bits):** Set to hex `7` (binary `0111`) at character index 14. - **Random Entropy (12 bits + 62 bits):** 74 bits of cryptographically secure random entropy draw from `crypto.getRandomValues`, preventing key prediction and collisions. - **Variant (2 bits):** Fixed to binary `10` at character index 19 (hex characters `8`, `9`, `a`, or `b`).
### Worked Comparison Example
Contrasting UUIDv4 vs UUIDv7 generated simultaneously: - **Standard UUIDv4 (Random):** `9c852d7e-128a-4c22-b5b6-7f45c90b0e91` (Unordered; inserts cause random database index fragmentation). - **Modern UUIDv7 (Time-Ordered):** `01918a3e-4b21-7f89-8d12-3c8a9140e567` (Chronologically sorted; sequential B-Tree inserts preserve contiguous disk pages). - Notice how the UUIDv7 prefix `01918a3e-4b21` represents the millisecond timestamp, guaranteeing subsequent records naturally sort after earlier records.
### Pure Client-Side Computation
All UUIDv7 identifiers are assembled directly inside your browser session using native `Date.now()` and `crypto.getRandomValues()`. No timestamps, generated keys, or environment parameters leave your device.
How to Use
- 1
Select UUIDv7 as your active identifier version (or toggle to UUIDv4 for legacy testing).
- 2
Choose the batch count (e.g., 1, 5, 10, or 25 identifiers per draw).
- 3
Click "Generate" to draw fresh timestamp-ordered UUIDv7 strings.
- 4
Click "Copy All" to copy the generated list directly into your database seeding scripts or ORM migrations.
Frequently Asked Questions
Why is UUIDv7 superior to UUIDv4 for PostgreSQL, MySQL, and SQLite database keys?
Because UUIDv4 is completely random, inserting new rows forces database engines to insert index nodes into random B-Tree pages, causing heavy cache eviction and write amplification. UUIDv7 appends sequentially to the rightmost leaf page, dramatically increasing write throughput.
Can a client's local system clock skew affect UUIDv7 ordering?
UUIDv7 uses standard millisecond timestamps. While severe local clock drift can alter relative generation order, each identifier remains globally unique due to its 74 bits of cryptographic entropy.
Are any generated keys stored or monitored on your servers?
No. All UUIDv7 generation takes place locally inside your browser runtime. Zero keys or timestamps are transmitted over the network.