UUID v4 Generator: What It Is, How It Works, and How to Use One

Created on 26 October, 2025 • Generator Tool • 4 views • 4 minutes read

Discover the best UUID v4 generator online for secure, random unique identifiers. Learn how to generate UUID v4, its benefits, and code examples for developers.

Overview
A UUID v4 generator creates 128-bit identifiers using cryptographically secure randomness. The result is a globally unique string like 3f1eab1e-5bbf-4e28-8a15-8a3b1b74d4a2 that you can safely use as IDs in databases, APIs, events, and files—without central coordination.
What is a UUID v4?

* UUID stands for Universally Unique Identifier (also called GUID in some ecosystems).
* Version 4 is the “random” flavor defined by RFC 4122.
* It contains 32 hexadecimal characters displayed in five groups: 8-4-4-4-12 (36 characters with hyphens).
* Two fields are reserved:

Version nibble: the 13th hex digit is always 4.
Variant bits: the first hex digit of the fourth group is 8, 9, a, or b.


* That leaves 122 bits of true randomness (128 total − 4 version − 2 variant).

Why developers use a UUID v4 generator

* Collision resistance: With 122 random bits, the space is about 5.3×10^36. Even generating 1 billion UUIDs, the collision chance is ~9.4e‑20—astronomically small.
* No coordination: You can generate IDs on any machine, online or offline, without calling a central service.
* Privacy: Unlike time/MAC‑based IDs (e.g., classic v1), v4 doesn’t leak host or timestamp data.
* Portability: Works across programming languages, storage engines, and message queues.

Anatomy of a valid UUID v4

* Format: xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx

x is any hex digit 0–9 or a–f
y is 8, 9, a, or b (variant field)


* Quick validation regex (case-insensitive):

^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$



How a good UUID v4 generator works

* Uses a CSPRNG (cryptographically secure pseudo‑random number generator).
* Sets version and variant bits per RFC 4122.
* Outputs lowercase hex by default and includes hyphens for readability.
* Avoids predictable sources (e.g., Math.random in JS).

Security notes

* UUIDs are identifiers, not secrets. Don’t treat them as passwords or tokens.
* If exposure matters (e.g., user IDs in URLs), still enforce authorization checks; “unguessable” is not a security control.
* If you need signed/opaque references, pair UUIDs with signed tokens (JWT/PASETO) or use short-lived, capability-based links.

Where UUID v4 shines

* Distributed systems and microservices
* Event IDs, correlation IDs, request tracing
* File/object names in storage buckets
* Primary keys when order doesn’t matter

When to consider other versions

* UUID v7 (time-ordered + randomness): friendlier to database indexes because IDs are monotonic over time.
* UUID v5 (name-based): deterministic IDs from a name + namespace (e.g., the same input always yields the same ID).
* Short IDs for UX: If you need human-friendly short codes, keep a mapping layer; don’t truncate UUIDs.

Database and performance tips

* Storage: Prefer binary storage when possible (BINARY(16) in MySQL, BYTEA in Postgres) for speed and space; convert to/from text at the edge.
* Indexing: Random v4 values can fragment B‑tree indexes. If write amplification is a concern, consider UUID v7 or use a secondary, ordered key for clustering.
* Serialization: Keep lowercase hex with hyphens for consistency in logs and payloads.

Copy‑paste code examples
JavaScript (Browser)
javascriptDownloadCopy code// Modern browsers
const id = crypto.randomUUID();
console.log(id); // 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'
JavaScript (Node.js)
javascriptDownloadCopy codeimport { randomUUID } from 'crypto';
const id = randomUUID();
console.log(id);
Python
pythonDownloadCopy codeimport uuid
print(str(uuid.uuid4()))
# or without hyphens:
print(uuid.uuid4().hex)
Go
goDownloadCopy code// go get github.com/google/uuid
package main

import (
"fmt"
"github.com/google/uuid"
)

func main() {
id := uuid.New() // v4
fmt.Println(id.String())
}
Rust
rustDownloadCopy code// Cargo.toml: uuid = { version = "1", features = ["v4"] }
use uuid::Uuid;

fn main() {
let id = Uuid::new_v4();
println!("{}", id);
}
PostgreSQL
sqlDownloadCopy code-- Option 1: pgcrypto (preferred in newer releases)
SELECT gen_random_uuid();

-- Option 2: uuid-ossp extension
CREATE EXTENSION IF NOT EXISTS "uuid-ossp";
SELECT uuid_generate_v4();
Shell
bashDownloadCopy code# Linux/macOS
uuidgen -r # ensure random (v4)
Common mistakes to avoid

* Using non‑secure RNGs: In JavaScript, Math.random() is not suitable.
* Truncating UUIDs: Cutting characters destroys collision guarantees; if you need shorter IDs, design a separate, encoded format with enough entropy.
* Mixing versions unknowingly: Some DBs or utilities default to v1 or vendor GUID variants; verify you’re generating v4 if that’s your standard.
* Treating UUIDs as secrets: Use proper auth; do not rely on obscurity.

Testing and validation checklist

* Confirm your generator uses a CSPRNG.
* Verify the version nibble (digit 13) is always 4.
* Verify the variant (first digit of group 4) is 8, 9, a, or b.
* Run a quick uniqueness test across a large sample to catch accidental formatting or RNG bugs.
* Decide on lowercase vs uppercase and stick to one style across services.

FAQ
Is a UUID v4 truly unique?
Practically, yes. With 122 random bits, the collision odds for typical scales are effectively zero. As with any probabilistic system, the risk rises with astronomical volumes, but it’s negligible for real-world apps.
Should I use UUID v4 as a primary key?
It’s fine for many systems. For write‑heavy, index‑sensitive databases, consider UUID v7 (time‑ordered) or store v4 as BINARY(16) and use a clustered surrogate key to reduce index churn.
Are hyphens required?
No. Hyphens improve readability but aren’t required by the binary format. Some APIs prefer hyphenless 32‑char hex; choose a single canonical style.
How do I generate millions safely and fast?
Use the language’s built‑in secure API (examples above), reuse RNG contexts when possible, and batch operations. For databases, avoid generating in SQL loops if it becomes a bottleneck; generate in the application layer.
Bottom line
A UUID v4 generator is the fastest path to globally unique, coordination‑free IDs. Use a cryptographically secure RNG, validate the version/variant bits, store in a compact form when possible, and choose v4 or v7 based on indexing needs. With these best practices, you get reliable identifiers that scale from side projects to planet‑size systems.
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