Browser JavaScript
const id = crypto.randomUUID();UUID v4 Generator
Your UUID v4
Generated privately on this device. Advanced format and batch controls are below.
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Batch and format options
Enter a whole number from 1 to 10,000.
Case, hyphens, braces, URN, quotes, prefix, and suffix change each displayed and exported value. JSON always uses valid JSON string quoting. A prefix or suffix wraps the identifier, so the result is no longer a canonical UUID.
Batch output
Press Ctrl/Cmd + Enter to regenerate with the current settings. Large output is kept in this scrollable field for responsive rendering.
Validate and decode a UUID
Paste a canonical, braced, compact, or urn:uuid: value. Wrapping prefixes or suffixes are not part of a UUID and are not accepted.
Validation runs locally as you type.
Enter a UUID to see its version, variant, and canonical form.
How UUID v4 works
A UUID is a 128-bit identifier. Under RFC 9562 §5.4, UUID v4 contains 122 random bits: random_a, random_b, and random_c. The remaining six bits identify version 4 and the RFC UUID variant. RFC 9562 superseded RFC 4122.
random_a 48 random bits
version 4 bits = 0100
random_b 12 random bits
variant 2 bits = 10
random_c 62 random bits
The canonical pattern is xxxxxxxx-xxxx-4xxx-Nxxx-xxxxxxxxxxxx, where N is 8, 9, a, or b. The hyphens are display separators, not old-style time, clock, or node data. UUID v4 embeds neither a timestamp nor a MAC address.
Local randomness and security
This page feature-detects crypto.randomUUID() and validates its result. If unavailable, it uses crypto.getRandomValues(), then sets and validates the v4 version and variant bits. If neither secure API is available, the tool shows an error and does not generate values. Nothing is uploaded.
Cryptographically strong randomness makes v4 useful for opaque distributed IDs, but a UUID should not automatically replace a purpose-built API key, password-reset token, session secret, or authorization credential. Adding a prefix or suffix creates a wrapped identifier rather than a canonical UUID.
Last reviewed: .
UUID v4 collision probability
With 2122 possible random values, the birthday-bound approximation for small probabilities is p ≈ n(n−1) / (2 × 2122). Near 50%, use p ≈ 1 − exp(−n(n−1)/(2 × 2122)).
| UUIDs generated | Approximate collision probability |
|---|---|
| 1 million (106) | 9.4 × 10−26 |
| 1 billion (109) | 9.4 × 10−20 |
| 1 trillion (1012) | 9.4 × 10−14 |
| About 2.71 × 1018 | 50% |
At one million UUIDs per second, reaching the 50% threshold would take roughly 85,700 years. Actual collision risk also depends on a correctly implemented random source.
UUID v4 vs UUID v7
| Consideration | UUID v4 | UUID v7 |
|---|---|---|
| Core data | Random | Unix timestamp plus random data |
| Chronological sorting | No | Yes |
| Creation-time privacy | Does not reveal time | Reveals approximate creation time |
| Distributed generation | Excellent | Excellent with a correct implementation |
| B-tree index locality | Random inserts can fragment indexes | Time ordering usually improves locality |
Choose v4 for opaque distributed identifiers. In write-heavy databases, v7 can be preferable because chronologically ordered inserts reduce B-tree fragmentation. “GUID” is common Microsoft terminology, not a fundamentally different kind of identifier; in most modern contexts it refers to the same 128-bit UUID format.
Generate UUID v4 in code
Node.js
const { randomUUID } = require('node:crypto');
const id = randomUUID();Python
import uuid
id = uuid.uuid4()Java
import java.util.UUID;
UUID id = UUID.randomUUID();C#
using System;
Guid id = Guid.NewGuid();Go (google/uuid)
import "github.com/google/uuid"
id := uuid.NewString()PostgreSQL
SELECT gen_random_uuid();MySQL: its built-in UUID() function does not guarantee UUID v4. Generate v4 in application code or use a carefully reviewed database-side implementation.
UUID v4 FAQ
Can UUID v4 values collide?
Yes in theory, but the 122 random bits make a collision extraordinarily unlikely. About 2.71 × 10¹⁸ generated UUID v4 values are needed for a 50% collision probability.
Does UUID v4 contain a timestamp or MAC address?
No. UUID v4 contains random data plus fixed version and variant bits; it does not encode a timestamp or MAC address.
Are GUID and UUID the same?
GUID is common Microsoft terminology for this family of 128-bit identifiers. In most modern developer contexts, GUID and UUID refer to the same textual identifier format.
Is UUID v4 suitable for database keys?
Yes, especially for opaque distributed IDs. Random v4 inserts can fragment B-tree indexes in write-heavy databases, so UUID v7 may offer better index locality.
How do I validate a UUID?
Normalize an optional urn:uuid: prefix, braces, and compact form, then verify 32 hexadecimal digits. For UUID v4, the version nibble must be 4 and the variant nibble must be 8, 9, a, or b.
Which characters can the UUID variant position contain?
For the RFC 9562 UUID variant, the first character of the fourth group is 8, 9, a, or b (case-insensitive).
Is UUID generation on this page private?
Yes. Generation and validation run locally in your browser using Web Crypto; values are not sent to this site.
When should I choose UUID v7 instead of v4?
Choose v7 when chronological sorting and database index locality matter. Choose v4 when you want a fully random, opaque identifier with no embedded creation time.