UUID Generator

How to generate UUIDs online

jsonsql.dev generates UUIDs instantly in your browser. No data is sent to any server — your UUIDs are created locally using the Web Crypto API.

Example

UUID v4 (random):

f47ac10b-58cc-4372-a567-0e02b2c3d479

UUID v7 (timestamp-based, sortable):

0190d4a8-7b3c-7f12-9a4e-5c1d2e3f4a5b

Batch output (5 UUIDs):

550e8400-e29b-41d4-a716-446655440000
6ba7b810-9dad-41d9-80b4-00c04fd430c8
7c9e6679-7425-40de-944b-e07fc1f90ae7
a0eebc99-9c0b-4ef8-bb6d-6bb9bd380a11
b9f8c3d2-1a4e-4f6b-8c7d-9e0f1a2b3c4d

Features

• Generate UUID v4 (random) using the Web Crypto API — cryptographically secure
• Generate UUID v7 (timestamp-based) — time-sortable, ideal for database primary keys
• Batch generate 1 to 100 UUIDs at once
• Format options: lowercase, UPPERCASE, or no dashes
• Copy individual UUIDs or copy all at once
• Validate any UUID — check if it's valid, detect the version
• Parse UUID v7 timestamps — extract the embedded date and time
• Dark and light theme support
• Works offline — no internet needed after the page loads
• 100% client-side — no data sent to any server

UUID v4 vs UUID v7

UUID Generator vs other tools

UUID versions explained

UUIDs (Universally Unique Identifiers) come in several versions, each with different generation strategies. Here is a comprehensive overview of the most important versions.

UUID v1 — timestamp + MAC address

UUID v1 combines a 60-bit timestamp (100-nanosecond intervals since October 15, 1582) with the node's MAC address. While this guarantees uniqueness across machines, it raises a privacy concern: anyone who reads a v1 UUID can extract the creator's MAC address and the exact time it was generated. For this reason, UUID v1 is rarely used in modern applications.

UUID v4 — fully random

UUID v4 is the most widely used version. It generates 122 random bits (the remaining 6 bits encode the version and variant), giving an astronomically large keyspace. UUID v4 requires no coordination between systems — any machine can generate one independently with virtually zero collision risk.

UUID v4 generates 122 random bits, giving 2^122 (5.3 x 10^36) possible values. The probability of generating a duplicate is astronomically low — you'd need to generate 1 billion UUIDs per second for 86 years to have a 50% chance of one collision.

UUID v7 — timestamp + random (the future)

UUID v7 was standardized in RFC 9562 (2024). It embeds a 48-bit Unix millisecond timestamp in the first 48 bits, followed by 74 random bits. This makes UUID v7 naturally sortable by creation time — a critical advantage for database indexing.

Why v4 is the most common today: it has been the standard since RFC 4122 and is supported everywhere. Why v7 is the future: it solves v4's biggest weakness (random index fragmentation) while maintaining the same ease of generation. Major databases like PostgreSQL 17+ now support native UUID v7 generation.

UUID v4 vs UUID v7: which should I use?

UUID v7 embeds a Unix millisecond timestamp in the first 48 bits, making UUIDs naturally sortable by creation time. This dramatically improves database index performance compared to random UUID v4.

Rule of thumb: Use UUID v7 for database primary keys and anything that benefits from time-ordering. Use UUID v4 when you need maximum privacy (no embedded timestamp) or when compatibility with older systems matters.

Using UUIDs as database primary keys

UUIDs are increasingly popular as database primary keys, especially in distributed systems. Here are the trade-offs.

Advantages

• Globally unique — no central authority or coordination needed between services
• Merge-friendly — combine data from multiple databases without ID conflicts
• Non-sequential — attackers cannot guess or enumerate IDs (with v4)
• Generate anywhere — clients can create IDs before inserting, no round-trip needed

Disadvantages

• Larger size — 16 bytes vs 4 bytes (int) or 8 bytes (bigint)
• Index fragmentation (v4) — random UUIDs cause random B-tree inserts, increasing page splits and slowing writes by 2-10x
• Harder to debug — f47ac10b-58cc-4372-a567-0e02b2c3d479 is less readable than 42
• JOIN performance — comparing 16-byte keys is slower than comparing 4-byte integers

Why UUID v7 solves the index problem

UUID v7's timestamp prefix means new UUIDs are always larger than older ones. In a B-tree index, this causes sequential appends rather than random inserts — the same pattern as auto-increment integers. Benchmarks show UUID v7 achieves write performance within 5-15% of auto-increment, while UUID v4 can be 2-10x slower.

UUID vs ULID vs nanoid

UUID format and structure

A UUID is a 128-bit identifier represented as 32 hexadecimal characters in 5 groups separated by hyphens, following the pattern 8-4-4-4-12.

f47ac10b-58cc-4372-a567-0e02b2c3d479
│        │    │    │    │
│        │    │    │    └── Node (48 bits)
│        │    │    └── Clock sequence (14 bits) + Variant (2 bits)
│        │    └── Version (4 bits) + Time/random (12 bits)
│        └── Time or random (16 bits)
└── Time or random (32 bits)

Version bits

The version is encoded in the 4 most significant bits of byte 6 (the 13th hex character, position index 14 in the string including hyphens). For example, a UUID starting with xxxxxxxx-xxxx-4xxx-... is version 4.

Variant bits

The variant is encoded in the 2-3 most significant bits of byte 8 (the 17th hex character). For RFC 9562 UUIDs, the two most significant bits are 10, meaning the hex digit is one of 8, 9, a, or b.

Special UUIDs

• Nil UUID: 00000000-0000-0000-0000-000000000000 — all zeros, used as a "not set" placeholder
• Max UUID: ffffffff-ffff-ffff-ffff-ffffffffffff — all ones, defined in RFC 9562

Generating UUIDs in different languages

Here is how to generate UUIDs in the most popular programming languages and tools.

JavaScript

// UUID v4 — built-in (Node 19+, all modern browsers)
const id = crypto.randomUUID();
// "f47ac10b-58cc-4372-a567-0e02b2c3d479"

Python

import uuid

# UUID v4
id = uuid.uuid4()
# UUID('f47ac10b-58cc-4372-a567-0e02b2c3d479')

# UUID v7 (Python 3.14+)
id = uuid.uuid7()

Go

import "github.com/google/uuid"

// UUID v4
id := uuid.New()
// "f47ac10b-58cc-4372-a567-0e02b2c3d479"

// UUID v7
id, _ := uuid.NewV7()

PostgreSQL

-- UUID v4 (built-in since PostgreSQL 13)
SELECT gen_random_uuid();

-- UUID v7 (built-in since PostgreSQL 17)
SELECT uuidv7();

Command line

# macOS / Linux
uuidgen

# Linux (lowercase)
cat /proc/sys/kernel/random/uuid

Related tools

Frequently asked questions