UUID Generator & Decoder

What Is a UUID?

// Generate a UUID v4 using the Web Crypto API
const uuid = crypto.randomUUID();
console.log(uuid);
// → '550e8400-e29b-41d4-a716-446655440000'

// Manual v4 generation with crypto.getRandomValues()
function generateUUIDv4() {
  const bytes = new Uint8Array(16);
  crypto.getRandomValues(bytes);
  bytes[6] = (bytes[6] & 0x0f) | 0x40; // version 4
  bytes[8] = (bytes[8] & 0x3f) | 0x80; // variant 10
  const hex = Array.from(bytes, b => b.toString(16).padStart(2, '0')).join('');
  return `${hex.slice(0,8)}-${hex.slice(8,12)}-${hex.slice(12,16)}-${hex.slice(16,20)}-${hex.slice(20)}`;
}

Key Features

UUID Version Comparison

Choose the right UUID version for your use case.

UUID vs Other ID Formats

UUID Version Examples

550e8400-e29b-41d4-a716-446655440000

01906b5e-4a3e-7234-8f56-b8c12d4e5678

6ba7b810-9dad-11d1-80b4-00c04fd430c8

886313e1-3b8a-5372-9b90-0c9aee199e5d

How to Use

1. 1

   Select UUID Version

   Choose from v1 (time-based), v3 (MD5 name-based), v4 (random), v5 (SHA-1 name-based), or v7 (time-ordered random). Each version serves a different purpose — v4 is the most common for general use.

2. 2

   Configure Options

   For v3 and v5, select a namespace (DNS, URL, OID, X.500, or custom) and enter a name to hash. Set the quantity from 1 to 50 and choose an output format: standard lowercase, UPPERCASE, no hyphens, or braces {GUID}.

3. 3

   Generate UUIDs

   Click the Generate button. Each UUID is created using the Web Crypto API (crypto.getRandomValues()) for cryptographic security. Version-specific fields like timestamps (v1/v7) and hashes (v3/v5) are correctly encoded.

4. 4

   Copy and Use

   Click the Copy button next to any UUID to copy it to your clipboard, or use Copy All to grab every generated UUID at once. Switch to the Decode tab to analyze an existing UUID's version, variant, timestamp, and other embedded information.

Common Use Cases

Database Primary Keys

Use UUID v4 or v7 as unique primary keys without coordination between database nodes. UUID v7 is especially well-suited because its time-ordered property improves B-tree index performance.

Distributed Systems

Generate unique identifiers independently across microservices, message queues, and event sourcing systems. UUIDs eliminate the need for a centralized ID-generation service.

API Development

Create unique request IDs, correlation IDs, and idempotency keys for RESTful and GraphQL APIs. UUIDs make it easy to trace requests across distributed service boundaries.

Session & Token Management

Generate unique session identifiers and temporary tokens for authentication flows. UUIDs provide sufficient uniqueness to prevent session collisions across large user bases.

Testing & Development

Quickly generate test data, mock identifiers, and unique fixture IDs for automated testing. Batch generation makes it easy to populate development databases and test suites.

Technical Details

UUID Structure

A UUID is 128 bits (16 bytes) represented as 32 hexadecimal characters in the 8-4-4-4-12 format. Bits 48-51 (the 13th hex digit) encode the version number. Bits 64-65 encode the variant field, which identifies the UUID layout. The remaining bits carry version-specific payload: timestamp, random data, or hash output.

Version Bits

Bits 48-51 (the high nibble of the 7th byte) encode the UUID version: 0001 = v1 (time-based), 0011 = v3 (MD5 name-based), 0100 = v4 (random), 0101 = v5 (SHA-1 name-based), 0110 = v6 (reordered time), 0111 = v7 (Unix epoch time). These four bits are always set explicitly during generation.

Variant Field

Bits 64-65 (the two most significant bits of the 9th byte) define the variant. The pattern 10x indicates RFC 4122/9562 UUIDs (the vast majority). Pattern 110 indicates Microsoft GUIDs with mixed-endian byte order. Pattern 0xx indicates NCS backward-compatible UUIDs (legacy). Pattern 111 is reserved for future use.

RFC 9562 Standard

RFC 9562, published in May 2024, supersedes RFC 4122 as the definitive UUID specification. It formally introduces UUID versions 6, 7, and 8. Version 6 reorders v1 fields for sortability. Version 7 uses a 48-bit Unix timestamp in milliseconds plus random data, making it the recommended version for new time-based UUIDs. Version 8 provides a format for custom, implementation-specific UUIDs. RFC 9562 also formally deprecates v1 in favor of v6/v7.

Best Practices

Choose the Right Version

Use v4 for general-purpose unique identifiers where no ordering or determinism is needed. Use v7 for database primary keys — its time-ordered property delivers significantly better index performance. Use v5 when you need deterministic IDs derived from names (prefer v5 over v3 for stronger hashing).

Use UUID v7 for Database Primary Keys

UUID v7's time-ordered structure keeps B-tree inserts sequential, reducing index fragmentation by approximately 90% compared to random v4 UUIDs. This translates to faster writes, smaller indexes, and better cache utilization. Most modern databases (PostgreSQL 17+, MySQL 8.0+) have native UUID support optimized for this pattern.

Never Use UUIDs as Security Tokens

UUIDs are designed for uniqueness, not secrecy. UUID v1 leaks the generation timestamp and MAC address. UUID v4 has only 122 bits of entropy with a predictable structure. For security tokens, API keys, or session secrets, use a dedicated CSPRNG to generate 128 or 256 bits of pure random data without the UUID structure overhead.

Validate Before Parsing

Always validate UUID format with a regular expression before parsing or storing. Reject malformed inputs at system boundaries — API endpoints, form submissions, and database inputs. This prevents injection attacks, data corruption, and hard-to-debug errors from invalid identifiers propagating through your system.

Frequently Asked Questions