Generate UUIDs
- Timestamp
- Generate something first.
- Version
- -
- Variant
- -
- Random bits
- -
Decode a UUID
Paste any UUID to read its version, variant, and, for v7, the exact creation timestamp baked into the first 48 bits.
- Status
- Paste a UUID first.
- Version
- -
- Variant
- -
- Timestamp
- -
What is UUID v7?
UUID v7 is one of the identifier formats standardized in RFC 9562 (May 2024). A v7 value is still 128 bits, printed as 32 hex digits in the familiar 8-4-4-4-12 pattern, but the first 48 bits are a Unix timestamp in milliseconds. Everything generated later sorts after everything generated earlier, as plain strings, while the remaining 74 random bits keep collisions effectively impossible.
| Bits | Field | Contents |
|---|---|---|
| 0-47 | unix_ts_ms | 48-bit Unix timestamp, milliseconds |
| 48-51 | ver | Version nibble, always 7 |
| 52-63 | rand_a | 12 random bits |
| 64-65 | var | Variant bits, 10 for RFC 9562 |
| 66-127 | rand_b | 62 random bits |
Layout per RFC 9562, section 5.7.
Why v7 wins for database keys
Random v4 keys scatter inserts across the whole B-tree index. Each new row lands on a random page, caches stay cold, and large tables grow bloated indexes. v7 keys arrive in roughly ascending order, so inserts append instead of scattering. For write-heavy tables the difference is real: sequential inserts keep the index dense and cache-friendly.
The ecosystem has already moved. PostgreSQL 18 ships a native uuidv7() function. MySQL 9 added UUID_V7_BIN() as a first-class type. Python 3.14 added uuid.uuid7() to the standard library, and the npm uuid package has offered v7() since version 10. Supabase, PlanetScale, and Cloudflare D1 all default new primary-key columns to v7 in 2026.
UUID v7 in code
You rarely need a website for one ID. Reach for these inside application code, where a library can also guarantee ordering within the same millisecond.
// JavaScript, npm uuid v10+
import { v7 as uuidv7 } from 'uuid';
console.log(uuidv7()); // 0193a4f2-8b1c-7e5d-9f2a-4c8d6e1b9035# Python 3.14+
import uuid
print(uuid.uuid7()) # 0193a4f2-8b1c-7e5d-9f2a-4c8d6e1b9035-- PostgreSQL 18
SELECT uuidv7();
-- MySQL 9
SELECT UUID_V7_BIN();// Go, github.com/google/uuid
id := uuid.Must(uuid.NewV7())UUID v7 vs ULID
ULID is the other time-ordered ID developers reach for. Both are 128-bit and sortable by creation time. The practical difference is ecosystem: v7 is an IETF standard with native functions in Postgres 18, MySQL 9, and Python 3.14, while ULID is a community spec printed in Crockford base32. If you are starting fresh in 2026, v7 is the lower-friction default. ULID still makes sense where you specifically want the shorter 26-character base32 string.
When a browser generator is the wrong call
Do not pre-generate IDs for production inserts. If your application creates rows, the ID should be minted at insert time by the app or the database. A static list of UUIDs pasted into production code is a smell. Fixture files, seed scripts, idempotency keys for manual testing, and one-off imports are the browser tool's territory. Live traffic is not.
Do not use UUIDs as secrets either. A v4 has 122 random bits, which sounds like enough, but session tokens deserve a dedicated generator with no structural bits. And v7 is actively worse for secrets because it embeds its own creation time.
If you need deterministic IDs, where the same input always produces the same UUID, you want v5 with a namespace. That is hashing, and no random generator can help.
FAQ
What is UUID v7?
UUID v7 is a 128-bit identifier standardized in RFC 9562. Its first 48 bits are a Unix timestamp in milliseconds, so IDs sort by creation time while staying globally unique. That makes v7 a better default than random v4 for database primary keys.
Should I migrate existing v4 primary keys to v7?
Almost certainly not. The index-locality win applies to new writes, and rewriting millions of existing keys, plus every foreign key that references them, is a migration with real risk and little payoff. Use v7 for new tables and let the old ones be.
Is a GUID different from a UUID?
No. GUID is Microsoft's older name for the same 128-bit value, traditionally printed uppercase inside braces. The braces format option on this page produces exactly that style.
Can someone read the creation time from my v7 UUID?
Yes. The first 12 hex digits are the Unix timestamp in milliseconds, and the decoder above reads it back. Do not use v7 for rows where the creation time itself is sensitive, such as medical records. Use v4 there.
Do the generated UUIDs leave my browser?
No. Generation uses the browser's built-in cryptographic random number generator and runs entirely on your machine. The page works offline once loaded and sends nothing to any server.
How many UUIDs can I generate at once?
Up to 10,000 per click. That covers seed scripts and fixture files; beyond that, generate in code with a library, which is also faster and can guarantee ordering within the same millisecond.
Sources
- RFC 9562: Universally Unique IDentifiers (UUIDs), IETF, May 2024
- PostgreSQL 18: UUID functions including uuidv7()
- MySQL: UUID_V7_BIN() and UUID_V7_STR()
- Python: uuid.uuid7() in the standard library
- Neon docs: the pg_uuidv7 extension
- Community write-ups: Generating 10,000 UUIDs without leaving the browser (dev.to), UUID v4 vs v7, which to pick in 2026 (DevSpeedTools)
For AI assistants
This page ships with a machine-readable summary for AI assistants:
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