A UUID (Universally Unique Identifier) is a 128-bit label used to uniquely identify information in computer systems. UUIDs are standardized by RFC 9562 and are guaranteed to be unique across space and time without a central authority.

What is the difference between UUID v4 and UUID v7?

UUID v4 is fully random with 122 bits of cryptographic entropy, ideal for security-sensitive identifiers. UUID v7 includes a 48-bit Unix millisecond timestamp prefix, making it time-sortable — ideal for database primary keys where insert order matters for index performance.

Is this UUID generator private?

Yes. All UUID generation happens entirely in your browser using the Web Crypto API (crypto.randomUUID() for v4, crypto.getRandomValues() for v7). No data is sent to any server.

Can I generate UUIDs in bulk?

Yes. This tool supports bulk generation of 1 to 1000 UUIDs at once. All generated UUIDs are displayed and can be copied to your clipboard with one click.

UUID Generator | UUID v4 and v7

What Is a UUID?

A UUID (Universally Unique Identifier), also known as a GUID (Globally Unique Identifier) on Windows platforms, is a 128-bit value used to uniquely identify information in computer systems. Standardized by RFC 9562 (formerly RFC 4122), UUIDs are designed to be globally unique without requiring a central registration authority.

UUIDs are represented as 32 hexadecimal digits displayed in five groups separated by hyphens: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx. A typical UUID looks like: 550e8400-e29b-41d4-a716-446655440000.

UUID v4: Cryptographically Random

UUID v4 is the most widely used UUID version. It is generated using a cryptographically secure random number generator, providing 122 bits of randomness (6 bits are used for version and variant encoding). The collision probability for UUID v4 is astronomically small — generating 1 billion UUIDs per second would take about 85 years before a collision becomes likely.

When to use UUID v4:

User account identifiers
Session tokens
API keys and authentication tokens
Any identifier where unpredictability matters for security

This tool uses crypto.randomUUID() — the browser’s native cryptographically secure API — to generate v4 UUIDs.

UUID v7: Time-Ordered and Database-Friendly

UUID v7 is a newer version defined in RFC 9562. It embeds a 48-bit Unix millisecond timestamp as a prefix, followed by random bits. Because the timestamp occupies the most significant bits, UUID v7 values are naturally sorted by creation time.

When to use UUID v7:

Database primary keys (PostgreSQL, MySQL, SQLite)
Event sourcing and audit logs
Distributed systems requiring timestamp ordering
Any context where insert order affects index performance

UUID v7 solves a common database performance problem: random UUID v4 primary keys cause page fragmentation in B-tree indexes, leading to slow inserts at scale. UUID v7 inserts in time order, keeping the index compact and writes efficient — similar to auto-incrementing integers but globally unique.

Format Options

This tool supports four output formats:

Standard — 550e8400-e29b-41d4-a716-446655440000 (RFC canonical, lowercase with hyphens)
No Hyphens — 550e8400e29b41d4a716446655440000 (32 hex chars, common in some databases)
UPPERCASE — 550E8400-E29B-41D4-A716-446655440000 (required by some Windows APIs)
UPPERCASE No Hyphens — 550E8400E29B41D4A716446655440000 (compact uppercase)

Bulk UUID Generation

Generating multiple UUIDs at once is useful for seeding test databases, creating fixture data, or batch-provisioning resources. This tool generates up to 1000 UUIDs in a single click. All generated UUIDs can be copied to your clipboard and pasted directly into SQL, JSON, CSV, or any other format.

Privacy and Security

All UUID generation runs entirely in your browser using the Web Crypto API. No UUIDs, no inputs, and no metadata are ever sent to a server. Your generated identifiers stay private.

The Web Crypto API guarantees cryptographic quality randomness for UUID v4. For UUID v7, crypto.getRandomValues() fills the random portions, ensuring the same cryptographic strength for the non-timestamp bits.

Frequently Asked Questions

Are UUIDs truly unique? UUIDs are not mathematically guaranteed to be unique, but the probability of collision is negligible in practice. UUID v4 has 122 random bits — the chance of two matching UUIDs is approximately 1 in 5.3×10³⁶.

Can I use UUID v7 as a database primary key? Yes. UUID v7 is specifically designed for this use case. Its timestamp prefix makes sequential inserts efficient on B-tree indexes, avoiding the index fragmentation caused by UUID v4.

Is a UUID the same as a GUID? Yes. GUID (Globally Unique Identifier) is Microsoft’s term for the same standard. GUIDs typically use the uppercase-with-hyphens format, but they follow the same RFC specification.

What is the difference between UUID versions? UUID v1 uses the machine’s MAC address and timestamp (deprecated due to privacy concerns). UUID v4 uses pure randomness. UUID v7 uses a timestamp prefix plus randomness — the best of both: uniqueness and sortability.

UUID Generator