A UUID (Universally Unique Identifier) is a 128-bit identifier standardized by RFC 9562. UUIDs are designed to be unique across space and time without requiring a central authority. They are formatted as 32 hexadecimal digits in five groups separated by hyphens: 8-4-4-4-12. UUIDs are also called GUIDs (Globally Unique Identifiers) in Microsoft ecosystems.

How likely is a UUID collision?

For UUID v4, which has 122 random bits, the probability of collision is astronomically low. You would need to generate about 2.71 quintillion (2.71 × 10^18) UUIDs to have a 50% chance of a single collision. In practical terms, generating 1 billion UUIDs per second for 85 years would give you only a 50% chance of one duplicate.

UUID Generator — Free Online UUID v4 & v7 Tool

Version

Count

Format

Click Generate or press Space to create UUIDs

Valid—

Version—

Variant—

Timestamp—

Standard Form—

Integer—

How to Use This Tool

Step 1

Pick version & count

Choose UUID v4 (fully random) or v7 (timestamp-prefixed for sortable IDs). Set how many you need — up to 100 at once.

Step 2

Choose a format

Standard (8-4-4-4-12), no hyphens, UPPERCASE, with {braces} for C#/.NET, or URN format (urn:uuid:...).

Step 3

Generate & copy

Click Generate or press Space. Click any UUID to copy it individually. Use Copy All for the full batch, or Copy Lines for newline-separated.

Step 4

Validate & parse

Switch to Validate to paste any UUID and see its version, variant, embedded timestamp (v1/v6/v7), and integer representation.

UUID Version Comparison

Quick reference for all UUID versions defined in RFC 9562 and their characteristics.

Version	Source	Sortable	Deterministic	Best For
v1	Timestamp + MAC address	Partially	Yes (same host)	Legacy systems, distributed logging
v3	MD5 hash of namespace + name	No	Yes	Deterministic IDs from names (e.g. DNS)
v4	Random / pseudo-random	No	No	General purpose, most widely used
v5	SHA-1 hash of namespace + name	No	Yes	Deterministic IDs (preferred over v3)
v6	Reordered v1 timestamp	Yes	Yes (same host)	Drop-in sortable replacement for v1
v7	Unix timestamp + random	Yes	No	Database PKs, modern distributed systems

Frequently Asked Questions

What is a UUID?

A UUID (Universally Unique Identifier) is a 128-bit identifier standardized by RFC 9562 (formerly RFC 4122). UUIDs are designed to be globally unique without requiring a central registration authority. They're formatted as 32 hex digits in five groups separated by hyphens: xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx where M indicates the version and N indicates the variant. The term GUID (Globally Unique Identifier) is the same concept used in Microsoft ecosystems.

What is the difference between UUID v4 and v7?

UUID v4 uses 122 bits of random data, making each UUID completely unpredictable with no inherent ordering. UUID v7 packs a Unix millisecond timestamp into the first 48 bits, followed by random data. This means v7 UUIDs sort chronologically by creation time, which is ideal for database primary keys — it preserves insertion order, reduces B-tree index fragmentation, and improves write performance, while still providing enough randomness (74 bits) to avoid collisions.

How likely is a UUID v4 collision?

Extraordinarily unlikely. UUID v4 has 122 random bits, giving 5.3 × 10³⁶ possible values. By the birthday paradox, you'd need to generate about 2.71 × 10¹⁸ (2.71 quintillion) UUIDs for a 50% collision probability. Generating 1 billion UUIDs per second, it would take about 85 years to reach that point. In any practical application, v4 collisions are effectively impossible.

Should I use UUID or auto-increment IDs in my database?

It depends on your architecture. Auto-increment IDs are simple, compact (4-8 bytes vs 16 for UUID), and naturally sortable, but they require a central authority (your database) and expose information about record count and creation order. UUIDs can be generated anywhere without coordination, making them ideal for distributed systems, microservices, and offline-capable apps. UUID v7 gives you the best of both worlds: decentralized generation with chronological sorting. The tradeoff is storage size (16 bytes) and slightly slower index lookups on some databases.

Is my data sent to a server?

No. All UUID generation and validation happens in your browser using JavaScript's crypto.getRandomValues() for cryptographically secure random numbers. Nothing is transmitted to any server.