UUID Generator

The Complete Guide to UUIDs and GUIDs

UUIDs (Universally Unique Identifiers), also called GUIDs (Globally Unique Identifiers) in Microsoft ecosystems, are 128-bit identifiers designed to be unique across all space and time without requiring central coordination. They are the foundation of distributed systems, microservices, database primary keys, and any system that needs to generate unique IDs without a central authority. Our free UUID Generator produces cryptographically secure v4 UUIDs instantly in your browser.

What is a UUID?

A UUID is a 128-bit value, typically displayed as 32 hexadecimal digits separated by hyphens in the 8-4-4-4-12 pattern:

550e8400-e29b-41d4-a716-446655440000

The format is defined by RFC 4122 and contains 5 groups: xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx where M indicates the UUID version and N indicates the variant.

UUID Versions Compared

UUID v1 (Time-Based)

Generated from the current timestamp and the machine's MAC address. Pros: sortable by creation time. Cons: reveals the generating machine's MAC address (privacy concern), requires coordination to avoid duplicates on the same machine in the same millisecond.

Use when: You need time-ordered UUIDs and don't mind exposing MAC address information.

UUID v3 (Name-Based, MD5)

Generated by hashing a namespace UUID and a name string using MD5. Deterministic: the same inputs always produce the same UUID.

Use when: You need the same UUID every time you refer to the same concept (e.g., a URL always maps to the same UUID).

UUID v4 (Random) — What Our Tool Generates

Generated using cryptographically strong random numbers. 122 bits of randomness (6 bits are used for version and variant markers).

Collision probability: To have a 50% chance of a single collision, you would need to generate 2.71 quintillion (2.71 × 10^18) UUIDs. At 1 billion UUIDs per second, that would take about 85 years. In practice, v4 UUID collisions are essentially impossible.

Use when: You need a random, unique identifier with no ordering requirement. This is by far the most commonly used UUID version.

UUID v5 (Name-Based, SHA-1)

Like v3 but uses SHA-1 instead of MD5. More collision-resistant than v3.

Use when: You need deterministic UUIDs (same as v3 use cases) and prefer SHA-1 over MD5.

UUID v7 (New Standard, 2022)

The newest version, defined in the 2022 update to RFC 4122. Combines a millisecond-precision Unix timestamp with random data, making v7 UUIDs sortable by creation time — the best of v1 and v4. Increasingly adopted by databases and ORMs.

UUIDs as Database Primary Keys

One of the most common uses of UUIDs is as database primary keys. Compared to auto-increment integers:

Advantages of UUID primary keys:

• No coordination needed: UUIDs can be generated client-side or in any microservice without querying the database first
• No sequential exposure: Auto-increment IDs reveal how many records exist (record #12345 means at least 12,345 orders exist). UUIDs reveal nothing.
• Globally unique: You can merge databases or move records between systems without ID conflicts
• Safe for distributed systems: Multiple services can generate IDs independently

Disadvantages of UUID primary keys:

• Storage: UUIDs take 16 bytes (or 36 bytes as strings) vs. 4 bytes for INT or 8 bytes for BIGINT
• Index fragmentation: Random v4 UUIDs cause index fragmentation in B-tree indexes, slowing INSERT performance at scale. Solution: use UUID v7 (time-ordered) instead.
• Readability: Much harder to read and debug than "User ID: 42"

UUID Format Variations

• Standard (with hyphens): 550e8400-e29b-41d4-a716-446655440000
• Without hyphens: 550e8400e29b41d4a716446655440000 — used in some databases and APIs
• Uppercase: 550E8400-E29B-41D4-A716-446655440000
• Braces (Microsoft GUID): {550e8400-e29b-41d4-a716-446655440000}

Use our free UUID Generator to create cryptographically secure v4 UUIDs in bulk. For generating secure tokens, also try our Password Generator and Hash Generator.