Should I use UUID v4 or v7 for database primary keys?

UUID v7 for new applications. Its time-sortable design means records insert in chronological order, dramatically improving index performance vs random v4.

A UUID (Universally Unique Identifier) is a 128-bit identifier standardized by RFC 4122. It is represented as 32 hexadecimal digits displayed in 5 groups separated by hyphens: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx.

How do I generate a UUID in JavaScript?

In modern browsers and Node.js 14.17+: crypto.randomUUID() generates a secure v4 UUID. For older environments use the uuid npm package: import { v4 as uuidv4 } from "uuid"; uuidv4().

How do I generate a UUID in Python?

Use the built-in uuid module: import uuid; str(uuid.uuid4()) for v4, or uuid.uuid1() for v1. For v7 (not yet in stdlib), use the uuid6 package: pip install uuid6.

How do I generate a UUID in PostgreSQL?

Use gen_random_uuid() (available since PostgreSQL 13) or the pgcrypto extension: SELECT gen_random_uuid(). For UUID v7 use a custom function or the pg_uuidv7 extension.

How do I validate a UUID format?

A valid UUID matches the pattern: /^[0-9a-f]{8}-[0-9a-f]{4}-[1-8][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i. Paste into our UUID Validator to check format and identify the version.

What is UUID v7 and why is it better for databases?

UUID v7 encodes a Unix millisecond timestamp in the first 48 bits, making IDs sort chronologically. This means database inserts are sequential rather than random, dramatically reducing index fragmentation and improving write performance compared to v4.

What is the difference between UUID and ULID?

ULID (Universally Unique Lexicographically Sortable Identifier) is 128-bit like UUID but encoded in Crockford Base32 (26 chars vs 36 for UUID). ULIDs are time-sortable by default and URL-safe. UUID v7 achieves similar time-sortability while maintaining the standard UUID format.

How do I generate a UUID without hyphens?

Generate a UUID and remove the hyphens: uuid.replaceAll("-", "") in JavaScript. Or: uuid.uuid4().hex in Python. Some databases (MySQL, MongoDB) store UUIDs without hyphens in BINARY(16) columns for efficiency.

All tools

UUID / GUID Generator

Generate v1–v8, validate, analyze, compare, collision probability, and export (JSON/CSV/SQL). 100% client-side — no UUID data sent to servers.

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Runs in browserNo UUID data sent to serverCryptographically secure

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Format

HyphenatedUppercaseURN

UUID Analyzer

Validator

Compare two UUIDs

Collision probability

UUIDs →1.00e+2%

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What Is a UUID?

A UUID (Universally Unique Identifier) is a 128-bit label used to identify information in computer systems. Standardised in RFC 4122, a UUID looks like:

xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx

M indicates the version; N indicates the variant. UUIDs are used as database primary keys, session IDs, transaction IDs, and anywhere a globally unique identifier is needed without coordination between systems.

How it works

Generate and Export UUIDs in Seconds

Choose a version

Pick v4 (random), v7 (time-sorted), v5 (namespace), or any other version.

Set quantity

Generate 1 or bulk-generate up to 1,000 UUIDs at once.

Copy or export

Copy individual UUIDs or export all to JSON, CSV, or SQL INSERT statements.

Validate or analyze

Paste any UUID to validate, inspect the version/variant, and check collision probability.

Use cases

When Developers Use UUIDs

🗄️

Database Primary Keys

Use v7 for time-sortable, index-friendly primary keys in Postgres, MySQL, or DynamoDB.

🔗

Distributed Systems

Generate IDs across services without a central coordinator — no collision coordination needed.

🔀

Idempotency Keys

Attach a v4 UUID to API requests to make retries safe without duplicate processing.

📂

File & Upload IDs

Name uploaded files with UUIDs to avoid collisions and prevent enumeration attacks.

🧪

Test Fixtures

Generate bulk UUIDs for seeding test databases or mock API responses.

🔁

Deterministic IDs

Use v5 (SHA-1 namespace) for stable, repeatable IDs from a URL or email.

UUID Versions Explained — v1 through v8

Version	Source	Sortable	Best for
v1	Timestamp + node	✅ Time	Legacy time-ordered systems
v3	MD5 namespace	—	Deterministic IDs (legacy)
v4	Random	—	Most general use cases
v5	SHA-1 namespace	—	Deterministic IDs (preferred over v3)
v6	Reordered v1	✅ Time	DB-friendly v1 replacement
v7	Unix ms + random	✅ Time	⭐ New apps, database primary keys
v8	Custom	App-defined	Application-specific layouts

UUID v4 vs v7 — Which to Use for Database Keys?

v7 for all new applications. UUID v7 encodes a Unix millisecond timestamp in the first 48 bits, making it time-sortable. Records with v7 primary keys insert in chronological order, which dramatically improves B-tree index performance compared to random v4 UUIDs (which scatter inserts across the index, causing page splits). Use v4 for non-database IDs where sort order does not matter.

FAQ

Frequently Asked Questions

1What is the difference between UUID and GUID?

They are the same thing. GUID is Microsoft's term for UUID. Both follow RFC 4122 and are completely interchangeable. GUID is common in Windows/.NET; UUID is used everywhere else.

2What is the difference between UUID v4 and v7?

v4 is purely random — 122 bits of randomness. v7 encodes a Unix millisecond timestamp in the first 48 bits making it time-sortable, which significantly improves database index performance.

3Can two UUIDs ever be the same?

Practically impossible. A v4 UUID has 2^122 possible values. To have a 50% collision chance you would need to generate approximately 2.7 quintillion UUIDs. Use the collision probability calculator in the tool to see exact probabilities for your scale.

4Should I use UUID or auto-increment for database IDs?

Auto-increment is simpler for single-database setups. UUIDs are better for distributed systems, offline ID creation, merging databases, and public APIs where you don't want to expose sequential IDs. UUID v7 minimises index fragmentation vs random v4.

5What is a namespace UUID (v3 and v5)?

Namespace UUIDs are deterministic — the same namespace and name always produce the same UUID. v3 uses MD5, v5 uses SHA-1. Use them when you want stable IDs from the same input (e.g. a URL or email address).

6Are the UUIDs generated here cryptographically secure?

Yes. v4 and v7 UUIDs use the Web Crypto API's getRandomValues(), which is a cryptographically secure random number generator. Nothing is sent to any server.

Learn more

Developer Guides

📖UUIDs in API Design 📖Unique IDs Best Practices 📖ID Strategies for Databases 📖Distributed Systems IDs

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