How It Works

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Cryptographically Random

Uses the Web Crypto API (crypto.getRandomValues) to generate truly random UUID v4 values. Every UUID is unique with 122 bits of randomness -- the probability of collision is astronomically low.

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Bulk Generation

Need multiple UUIDs at once? Use the slider to generate up to 100 UUIDs in a single click. Copy them all to your clipboard with one button or copy individual UUIDs from the list.

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Format Options

Customize the output to match your needs: uppercase or lowercase, with or without dashes, and optionally wrapped in braces for GUID-style formatting used in Windows and .NET applications.

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UUID Validation

Paste any UUID to validate its format, detect the version (v1-v5), identify the variant, and check RFC 4122 compliance. Instantly see if a UUID is well-formed or has issues.

Understanding UUIDs

A Universally Unique Identifier (UUID) is a 128-bit identifier standardized by RFC 4122. UUIDs are designed to be unique across space and time without requiring a central registration authority. They are widely used in distributed systems, databases, APIs, and software development to identify resources, records, transactions, and sessions.

UUID Format

xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx

A UUID is displayed as 32 hexadecimal digits arranged in five groups separated by hyphens: 8-4-4-4-12. The M nibble indicates the UUID version (1-5), and the top bits of the N nibble indicate the variant.

UUID Versions

Version 1: Based on timestamp and MAC address. Guarantees uniqueness but may expose the host's network address.
Version 2: DCE Security version, similar to v1 but includes POSIX UID/GID. Rarely used in practice.
Version 3: Generated from an MD5 hash of a namespace and name. Deterministic -- the same input always produces the same UUID.
Version 4: Randomly generated using 122 bits of randomness. The most commonly used version and what this tool generates.
Version 5: Like v3 but uses SHA-1 instead of MD5. Preferred over v3 for new applications needing name-based UUIDs.

How to Use This Tool

Click "Regenerate" to create a new UUID v4 instantly. Use the format options to switch between lowercase, uppercase, no-dash, or braces output. Adjust the bulk slider to generate up to 100 UUIDs at once. Switch to "Validate" mode to paste an existing UUID and check its format, version, and variant. All processing happens entirely in your browser using the Web Crypto API.

Common Use Cases

Database Primary Keys: Use UUIDs as primary keys to avoid sequential ID enumeration and enable distributed ID generation without coordination.
API Resource Identifiers: Assign UUIDs to API resources for globally unique, non-guessable identifiers in REST and GraphQL APIs.
Session Tokens: Generate unique session identifiers that are practically impossible to guess or collide with existing sessions.
File Naming: Use UUIDs to create unique file names for uploads, avoiding conflicts in storage systems.
Distributed Systems: Generate IDs independently on multiple nodes without a central authority or risk of collision.

Frequently Asked Questions

What is a UUID? ▼

A UUID (Universally Unique Identifier) is a 128-bit identifier standardized by RFC 4122. It is designed to be unique across all systems without requiring a central registration authority. UUIDs are represented as 32 hexadecimal digits displayed in five groups separated by hyphens (e.g., 550e8400-e29b-41d4-a716-446655440000). They are widely used in databases, APIs, and distributed systems to uniquely identify resources, records, and sessions. The term GUID (Globally Unique Identifier) is often used interchangeably with UUID, especially in Microsoft ecosystems.

What is the difference between UUID and GUID? ▼

UUID and GUID are essentially the same thing -- both refer to 128-bit identifiers used to uniquely identify information. "UUID" (Universally Unique Identifier) is the term used in the official RFC 4122 specification and is common in Unix/Linux ecosystems, while "GUID" (Globally Unique Identifier) is the term used by Microsoft in Windows, .NET, and COM. GUIDs are often displayed with braces, such as {550e8400-e29b-41d4-a716-446655440000}, and are typically uppercase. This tool supports both formats -- enable "Braces" and "Uppercase" options for GUID-style output.

How random is a UUID v4? ▼

A UUID v4 contains 122 bits of randomness (6 bits are used for the version and variant indicators). This produces approximately 5.3 x 10^36 possible UUIDs. To put that in perspective, you would need to generate about 2.71 quintillion (2.71 x 10^18) UUIDs to have a 50% probability of a single collision. This tool uses the Web Crypto API (crypto.getRandomValues), which provides cryptographically strong random values, making the generated UUIDs suitable for security-sensitive applications.

Can two UUIDs ever be the same? ▼

While theoretically possible, the probability of two randomly generated UUID v4 values colliding is extraordinarily small -- approximately 1 in 2^122 (about 5.3 x 10^36). For practical purposes, UUID v4 collisions are considered impossible. Even if you generated one billion UUIDs per second, it would take approximately 100 years to have a 50% probability of finding a single duplicate. This is why UUIDs are trusted as unique identifiers in distributed systems where coordination between nodes is impractical.

Are UUIDs good for database primary keys? ▼

UUIDs work well as primary keys in many scenarios, especially in distributed systems where you need to generate IDs independently on multiple nodes without coordination. They prevent sequential ID enumeration (which can be a security concern) and simplify data merging across systems. However, there are trade-offs: UUIDs are larger than integer IDs (16 bytes vs 4-8 bytes), random UUIDs can cause B-tree index fragmentation, and they are less human-readable. For relational databases with heavy write loads, consider UUID v7 (time-ordered) or ULID for better index performance while retaining global uniqueness.

What UUID versions does this tool detect? ▼

The validator detects UUID versions 1 through 5 as well as the Nil UUID (all zeros). Version 1 uses a timestamp and MAC address, version 2 is DCE Security, version 3 uses MD5 hashing with a namespace, version 4 is random, and version 5 uses SHA-1 hashing with a namespace. The tool also identifies the variant field, which indicates whether the UUID follows the RFC 4122 standard, the NCS backward-compatibility format, or the Microsoft reserved format.

Is this tool secure? Does my data leave the browser? ▼

Yes, this tool is completely secure. All UUID generation and validation happens entirely in your browser using client-side JavaScript. No data is sent to any server, and nothing is stored or logged. The random number generation uses the Web Crypto API (crypto.getRandomValues), which is a browser-native cryptographic random number generator. You can verify this by checking your browser's network tab -- no requests are made when generating or validating UUIDs.

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