utility calculator

UUID & GUID Generator with Copy-to-Clipboard

Generate cryptographically unique UUIDs (v4) and GUIDs in bulk with a structured bit-layout diagram and one-click clipboard copy.

Formula Verified by Dr. Arthur Pendelton, PhD

Quick actions: Save inputs, view saved runs, print, share, or export results

Saved Runs

Inputs

Configuration

Batch Count5

Uppercase Output

UUID Structure Anatomy

Deconstruct the 128-bit structure of the first generated UUID:

Time Low (32-bit):3866ed87

Time Mid (16-bit):5632

Time High & Version (16-bit):422a

Clock Seq & Variant (16-bit):959a

Node (48-bit):ca4eacc69117

Results

Generated UUID List

3866ed87-5632-422a-959a-ca4eacc69117
c1a8c37d-758d-4d6b-b4b4-22eac59e9619
d007fc4d-8109-4093-83e4-8499281a1855
ff80e36a-9db0-46b4-a11f-ee6bf1da57e3
5530a66b-a318-402a-bd6d-334372091d1d

Version

RFC 4122 Version 4 (Random)

Bookmark this UUID generator

Save this page for quick ID generation during API development, database design, and testing workflows.

Formula

RFC 4122 UUID Version 4 layout

UUID = TimeLow (32b) - TimeMid (16b) - TimeHighAndVersion (16b) - ClockSeqAndVariant (16b) - Node (48b)

A Version 4 UUID consists of 128 bits. It utilizes 122 cryptographically secure random bits, with 4 bits representing version and 2 bits representing the RFC variant.

Step by step

How the calculation works

1Adjust the slider to choose the number of UUIDs to generate at once.
2Toggle between lowercase and UPPERCASE formats.
3Click the "Regenerate" button to produce a fresh batch of unique IDs.
4Use the "Copy All" button to export the list directly to your clipboard.

Example

Example UUID Format

A typical version 4 UUID matches: f47ac10b-58cc-4372-a567-0e02b2c3d479. The digit 4 in the third block designates version 4.

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How to understand and use this calculator

What is a UUID?

A UUID (Universally Unique Identifier), also known as a GUID (Globally Unique Identifier), is a 128-bit label standardized by RFC 4122. UUIDs are formatted as 32 hexadecimal characters separated by hyphens into five groups: 8-4-4-4-12, for example: 550e8400-e29b-41d4-a716-446655440000.

The primary purpose of a UUID is to enable distributed systems to generate unique identifiers without a central coordinating authority. Unlike sequential database integers, UUIDs can be generated independently on any machine at any time with an astronomically small probability of collision.

UUIDs appear in almost every modern software system: database primary keys, API request IDs, session tokens, file names, transaction identifiers, and distributed tracing correlation IDs. The "Global" in GUID (Microsoft's terminology) emphasizes that the identifier is unique across all time and space.

UUID Versions and Their Differences

RFC 4122 defines five UUID versions. Version 1 (time-based) incorporates the system clock and MAC address to guarantee uniqueness, but may expose machine identities. Version 2 (DCE Security) is rarely used in practice. Version 3 (MD5 hash) and Version 5 (SHA-1 hash) are deterministic — they generate the same UUID for the same input namespace and name.

Version 4 (random) is the most widely used. It consists entirely of random or pseudo-random bits, with only the version number and variant bits fixed. The structure is: xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx, where the 4 marks the version field and y is one of 8, 9, A, or B (indicating the RFC 4122 variant).

A Version 4 UUID has 122 random bits. The probability of generating two identical UUIDs is astronomically small — approximately 1 in 2¹²² or 5.3 × 10³⁶. To have a 50% chance of a collision, you would need to generate 2.7 × 10¹⁸ UUIDs.

Cryptographic Security in UUID Generation

Standard pseudo-random number generators (PRNGs) like Math.random() in JavaScript are not cryptographically secure and should not be used for security-sensitive identifiers such as session tokens or API keys. For UUIDs v4, browsers expose the Web Crypto API (crypto.getRandomValues()) and Node.js provides crypto.randomUUID(), both of which use a cryptographically secure pseudo-random number generator (CSPRNG).

This calculator uses the Web Crypto API to generate all UUIDs, ensuring they are cryptographically random and unpredictable. The generated values are suitable for use as session identifiers, CSRF tokens, and similar security-sensitive contexts.

Despite their security properties, UUIDs should not be used as secret passwords or cryptographic keys. A 128-bit random value is strong for uniqueness and moderate for unpredictability, but dedicated key generation schemes (like 256-bit keys) are used for cryptographic secrets.

How to Use This UUID Generator

Drag the Batch Count slider to choose how many UUIDs to generate at once (1 to 50), and toggle Uppercase Output if your system expects capitalized hex digits. Click "Regenerate Batch" to produce a fresh set using the Web Crypto API.

The UUID Structure Anatomy panel breaks the first generated ID into its five RFC 4122 fields — Time Low, Time Mid, Time High & Version, Clock Seq & Variant, and Node — so you can see exactly where the version and variant bits live.

Worked Example: Reading a Version 4 UUID

The sample UUID f47ac10b-58cc-4372-a567-0e02b2c3d479 splits into five hyphen-separated groups of 8-4-4-4-12 hex digits. The third group, 4372, starts with the digit 4 — confirming this is a Version 4 (random) UUID.

The fourth group, a567, starts with "a" — one of the four valid RFC 4122 variant digits (8, 9, a, or b). Every UUID this generator produces will show a 4 in that same position and one of those four characters immediately after the third hyphen, regardless of how many times you regenerate the batch.

Related Calculators

This generator is part of a Developer Tools cluster. For other randomized or structured text output, try the Password Generator. To validate or format data you plan to store alongside a UUID, use the JSON Formatter & Validator.

Related concepts

Entropy

A measure of randomness or unpredictability in a value, critical for security-sensitive identifiers.

CSPRNG

Cryptographically Secure Pseudo-Random Number Generator — an algorithm that produces random numbers suitable for security applications.

ULID

A time-ordered, lexicographically sortable alternative to UUID, preserving insertion order in database indexes.

Frequently Asked Questions

What is the difference between UUID and GUID?+

UUID (Universally Unique Identifier) is the RFC 4122 standard term. GUID (Globally Unique Identifier) is Microsoft's trademarked name for the same concept. They are technically identical in format and purpose.

What is UUID Version 4?+

UUID v4 is generated entirely from random or cryptographically random bits, with only the version (4) and variant bits fixed. It is the most commonly used version for general-purpose identifiers.

Can two UUIDs ever be identical?+

Theoretically yes, but the probability is negligible. With 122 random bits, you would need to generate approximately 2.7 × 10¹⁸ UUIDs before having a 50% chance of a single collision.

Are UUIDs safe to use as database primary keys?+

Yes, with a caveat. UUIDs are not sequential, which can cause index fragmentation in B-tree indexes. UUID v7 (a newer time-ordered variant) or ordered UUIDs mitigate this performance concern while preserving global uniqueness.

What is the UUID format?+

A UUID is formatted as 8-4-4-4-12 hexadecimal characters: xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx, where M is the version digit and N indicates the variant.

Should I use uppercase or lowercase UUIDs?+

Both are valid. RFC 4122 recommends lowercase for output. Some systems like Windows and Microsoft SQL Server default to uppercase GUIDs. When comparing UUIDs, always normalize to the same case.

What does "nil UUID" mean?+

The nil UUID is a special-case UUID where all 128 bits are zero: 00000000-0000-0000-0000-000000000000. It is used as a sentinel value representing "no ID" or an uninitialized identifier.

Can I use UUIDs as API keys?+

UUID v4 can serve as API keys in many applications, as they are random and unpredictable. For high-security contexts, consider using longer tokens (e.g., 32 random bytes = 256 bits) encoded in base64 for increased entropy.

What is UUID Version 5?+

UUID v5 is deterministic: given the same namespace and name, it always produces the same UUID by hashing them with SHA-1. This is useful for generating consistent IDs for resources (e.g., always mapping "user@example.com" to the same UUID).

Are UUIDs indexed efficiently in databases?+

Random UUIDs (v4) cause scattered index insertions, which can reduce database write performance due to page splits in B-tree indexes. Using time-ordered UUIDs (like UUID v7 or ULID) maintains insertion-time ordering and improves index performance.

What is a ULID?+

A ULID (Universally Unique Lexicographically Sortable Identifier) is an alternative to UUID designed to be sortable by creation time. It is 128 bits encoded as 26 alphanumeric characters, with the first 48 bits being a millisecond timestamp.

What is the "variant" in a UUID?+

The variant field identifies the UUID format in use. RFC 4122 UUIDs use the variant bits 10xx in the 8th group's first byte (resulting in hex values 8, 9, A, or B as the first character of the third UUID segment).

How to understand and use this calculator

What is a UUID?

UUID Versions and Their Differences

Cryptographic Security in UUID Generation

How to Use This UUID Generator

Worked Example: Reading a Version 4 UUID

Related Calculators

Related concepts

Entropy

A measure of randomness or unpredictability in a value, critical for security-sensitive identifiers.

CSPRNG

Cryptographically Secure Pseudo-Random Number Generator — an algorithm that produces random numbers suitable for security applications.

ULID

A time-ordered, lexicographically sortable alternative to UUID, preserving insertion order in database indexes.

Frequently Asked Questions

What is the difference between UUID and GUID?+

What is UUID Version 4?+

UUID v4 is generated entirely from random or cryptographically random bits, with only the version (4) and variant bits fixed. It is the most commonly used version for general-purpose identifiers.

Can two UUIDs ever be identical?+

Theoretically yes, but the probability is negligible. With 122 random bits, you would need to generate approximately 2.7 × 10¹⁸ UUIDs before having a 50% chance of a single collision.

Are UUIDs safe to use as database primary keys?+

What is the UUID format?+

A UUID is formatted as 8-4-4-4-12 hexadecimal characters: xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx, where M is the version digit and N indicates the variant.

Should I use uppercase or lowercase UUIDs?+

Both are valid. RFC 4122 recommends lowercase for output. Some systems like Windows and Microsoft SQL Server default to uppercase GUIDs. When comparing UUIDs, always normalize to the same case.

What does "nil UUID" mean?+

The nil UUID is a special-case UUID where all 128 bits are zero: 00000000-0000-0000-0000-000000000000. It is used as a sentinel value representing "no ID" or an uninitialized identifier.

Can I use UUIDs as API keys?+

What is UUID Version 5?+

Are UUIDs indexed efficiently in databases?+

What is a ULID?+

What is the "variant" in a UUID?+

UUID & GUID Generator with Copy-to-Clipboard

Inputs

Configuration

UUID Structure Anatomy

Results

Bookmark this UUID generator

RFC 4122 UUID Version 4 layout

How the calculation works

Example UUID Format

Learn more about this calculation

Understanding Calculator Formulas: How DTC Turns Inputs into Results

How to Use Do The Calculation Calculators: A Practical Step-by-Step Guide

UUID & GUID Generator with Copy-to-Clipboard

Inputs

Configuration

UUID Structure Anatomy

Results

Bookmark this UUID generator

Key output metrics

Anatomy Character Distribution

How to understand and use this calculator

What is a UUID?

UUID Versions and Their Differences

Cryptographic Security in UUID Generation

How to Use This UUID Generator

Worked Example: Reading a Version 4 UUID

Related Calculators

Related concepts

Frequently Asked Questions

RFC 4122 UUID Version 4 layout

How the calculation works

Example UUID Format

Learn more about this calculation

Understanding Calculator Formulas: How DTC Turns Inputs into Results

How to Use Do The Calculation Calculators: A Practical Step-by-Step Guide

Key output metrics

Anatomy Character Distribution

How to understand and use this calculator

What is a UUID?

UUID Versions and Their Differences

Cryptographic Security in UUID Generation

How to Use This UUID Generator

Worked Example: Reading a Version 4 UUID

Related Calculators

Related concepts

Frequently Asked Questions