A UUID (Universally Unique Identifier) is a 128-bit value, conventionally written as 32 hexadecimal digits split into five groups by hyphens: 550e8400-e29b-41d4-a716-446655440000. It identifies a record or resource without needing a central authority to assign the next available number.

Is a UUID the same thing as a GUID?

Yes. GUID (Globally Unique Identifier) is Microsoft's name for the same 128-bit format defined by RFC 4122. The terms are used interchangeably across the industry — a value generated by this tool is valid wherever either term is used.

Why does this tool only generate version 4 and not version 1?

Version 4 is fully random and reveals nothing about the generating machine, whereas version 1 embeds a timestamp and the machine's MAC address, which is now considered an information leak in most contexts. Version 4 has become the default choice for general-purpose unique identifiers in virtually all modern frameworks and databases, which is why this tool focuses on it exclusively.

What is the actual probability of two UUID v4 values colliding?

With 122 random bits, there are about 5.3 × 10^36 possible values. Using the birthday-paradox approximation, you would need to generate roughly 2.71 quintillion UUIDs before the collision probability reached even 50%. At a sustained rate of one billion UUIDs per second, that would take over 85 years — for any realistic application, the risk is treated as zero.

Should I store a UUID as a string or as binary in my database?

For high-volume tables, storing UUIDs as a 16-byte BINARY(16) column instead of a 36-character CHAR(36) string roughly halves storage and can meaningfully improve index performance, since most database engines compare binary values faster than formatted hex strings. Many ORMs handle this conversion for you automatically if you specify a UUID/binary column type.

Why do some systems reject UUIDs used as a primary key for performance reasons?

Purely random v4 values scatter insertion order across a B-tree index, causing page splits and fragmentation on very large, high-write tables — unlike an auto-incrementing integer, which always appends to the end of the index. Newer time-ordered UUID formats (v6, v7) were designed specifically to address this by combining a sortable timestamp prefix with random bits, trading a small amount of unpredictability for better index locality.

Can I safely remove the hyphens from a UUID?

Yes. The hyphens are a formatting convention with no effect on the underlying 128-bit value — a UUID with hyphens removed still represents the exact same identifier and can be reconstructed by re-inserting hyphens at the standard 8-4-4-4-12 character positions.

Does uppercase versus lowercase change what a UUID represents?

No. Hex digits a through f and A through F represent the same values regardless of case, so 550e8400-e29b-41d4... and 550E8400-E29B-41D4... are identical UUIDs. RFC 4122 recommends lowercase for output, but most systems accept either case as input without issue.

Can I use this generator to create UUIDs for use as React keys?

It works, but for React list keys generated dynamically on every render, a lighter-weight incrementing counter or a stable field already present in your data is usually more appropriate — reserve full cryptographic UUIDs for identifiers that need genuine global uniqueness, such as database records, file names, or API resource IDs.

Is crypto.randomUUID() supported in all browsers?

It is available in all current versions of Chrome, Firefox, Safari, and Edge, but requires a secure context (HTTPS or localhost). This tool automatically falls back to a manual crypto.getRandomValues()-based implementation that produces an identical, standards-compliant result on any browser where the native method is unavailable.

UUID Generator — Generate UUID v4 Online Free

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What is UUID Generator?

UUID Generator is a free online tool that produces RFC 4122 version 4 UUIDs using crypto.randomUUID() where the browser supports it, falling back to a manual crypto.getRandomValues()-based implementation otherwise. Generate anywhere from 1 to 100 at once, toggle uppercase output, toggle hyphens on or off, and copy the entire batch or any single value in one click.

A UUID (Universally Unique Identifier, also called a GUID — Globally Unique Identifier — in Microsoft ecosystems, the two terms refer to the same 128-bit format) exists to solve a specific coordination problem: generating an identifier that is guaranteed unique without any central authority handing out the next available number. An auto-incrementing integer primary key works fine on a single database, but the moment you have multiple independent services, offline clients, or sharded databases all creating new records simultaneously, nobody can hand out sequential numbers without a coordination bottleneck. UUIDs sidestep this entirely — any machine, anywhere, with no network connection and no shared state, can generate an identifier so unlikely to collide with any other UUID ever generated that the probability is treated as zero for all practical purposes.

There are several UUID versions defined by RFC 4122, and they are not interchangeable in what they reveal or guarantee. Version 1 is time-based and incorporates the generating machine's MAC address, which made it useful historically for sortable identifiers but is now largely avoided because embedding a MAC address leaks identifying hardware information. Versions 3 and 5 are deterministic — they hash a namespace and a name together (MD5 for v3, SHA-1 for v5), so the same input always produces the same UUID, which is useful for generating a stable ID from an existing value like a URL or email address rather than for creating a new random one. Version 4, the version this tool generates exclusively, is the simplest and by far the most common in modern application development: it is 122 bits of pure randomness with no embedded machine information, no timestamp, and no dependency on external input, which is exactly what you want for a general-purpose unique identifier. Newer time-ordered variants (v6 and v7) exist in more recent specifications to combine v4-style randomness with a sortable timestamp prefix, addressing the database index fragmentation that purely random v4 values can cause on very large tables — this tool sticks to standard v4 since it remains the most broadly supported and requested format across programming languages and databases.

The math behind why v4 collisions are considered practically impossible is worth being concrete about: of the 128 total bits, 6 are fixed (4 bits set the version to 0100, 2 bits set the variant to 10), leaving 122 bits of actual randomness. That is roughly 5.3 × 10^36 possible values. Using the birthday-paradox approximation, you would need to generate about 2.71 quintillion UUIDs before the probability of a single collision reached just 50% — a rate of a billion UUIDs generated every second would still take over 85 years to reach that point. This is why UUID v4 is trusted as a primary key in distributed databases, a correlation ID in distributed tracing, and a resource identifier in public APIs without any deduplication check against existing values.

Generation here uses crypto.randomUUID(), a native browser method built directly on the same operating-system cryptographic random number generator used for TLS keys, available in all current browser versions. Where that method is unavailable, the fallback path draws 16 random bytes from crypto.getRandomValues() and manually sets the version and variant bits per the RFC 4122 specification, producing an identical result. Either path avoids Math.random(), which is not cryptographically secure and should never be used to generate identifiers that need genuine unpredictability. Everything runs locally with zero network calls.

How It Works

RFC 4122 version 4 lays out 128 bits as 32 hexadecimal characters grouped 8-4-4-4-12 and separated by hyphens. Of those bits, the four most significant bits of the seventh byte are fixed to 0100 to mark the UUID as version 4, and the two most significant bits of the ninth byte are fixed to 10 to mark the RFC 4122 variant — every other bit is filled with cryptographically secure randomness. When crypto.randomUUID() is available, the browser handles this entire process natively and returns a correctly formatted string directly. In the fallback path, the tool allocates a 16-byte Uint8Array, fills it via crypto.getRandomValues(), then patches byte index 6 with (byte & 0x0f) | 0x40 to set the version nibble and byte index 8 with (byte & 0x3f) | 0x80 to set the variant bits, before converting the bytes to a hex string and inserting hyphens at the standard positions. The uppercase and no-hyphens options are applied as a final string transformation after generation, so they never affect the underlying randomness.

How to Use

Set the quantity

Enter how many UUIDs you need, from 1 to 100, in the Count field.

Choose formatting options

Toggle Uppercase if your target system expects capital hex digits, and toggle Hyphens off if you need the compact 32-character form without separators.

Generate

Click "Generate UUIDs" to create the full batch instantly using cryptographically secure randomness — every value is a standards-compliant RFC 4122 version 4 UUID.

Review the list

Scan the generated values to confirm the format matches what your database, API, or configuration file expects.

Copy what you need

Click "Copy All" to grab the entire newline-separated batch, or click Copy next to any individual UUID to grab just that one value.

Who Uses This Tool

🗄️

Database Primary Keys

Generate UUID v4 values to use as primary keys in distributed databases where auto-increment would cause conflicts.

📦

Object Identity in Code

Create UUIDs for in-memory objects, components, or React keys to guarantee uniqueness without a central registry.

🔗

API Resource Identifiers

Use UUIDs as resource IDs in REST APIs to prevent sequential enumeration attacks on endpoints.

🧪

Test Data Generation

Generate batches of UUIDs to populate test fixtures with realistic-looking unique identifiers.

📁

Unique File Naming

Use UUIDs as filenames for user-uploaded files to prevent collisions on shared storage buckets.

🔐

Session Token Seeding

Generate a UUID v4 as the base for session tokens or correlation IDs in distributed tracing systems.

Why Choose This Tool

RFC 4122 Compliant

Generated UUIDs strictly follow RFC 4122 v4 format with correct version (4) and variant (10xx) bits set.

Bulk Generation

Generate up to 100 UUIDs at once with a single click for batch operations and test data creation.

Cryptographically Random

Uses crypto.randomUUID() or crypto.getRandomValues() for 122 bits of true randomness per UUID.

Format Options

Toggle uppercase output and hyphen removal to match the format expected by your specific database or system.

Copy All Feature

Copy every generated UUID to the clipboard as a newline-separated list for easy pasting into scripts or seed files.

Instant and Private

All UUIDs are generated in your browser with no server calls, ensuring fast results and complete privacy.

Key Benefits

Generates standards-compliant RFC 4122 version 4 UUIDs

Uses the native crypto.randomUUID() API with a secure getRandomValues() fallback

Generate 1 to 100 UUIDs in a single batch

Independent toggles for uppercase output and hyphen removal

Copy the entire batch at once or copy any single UUID individually

122 bits of true randomness per UUID — collision risk is effectively zero

No Math.random() anywhere — every value uses a cryptographic entropy source

100% client-side — no identifiers are ever logged or transmitted

Frequently Asked Questions

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UUID Generator

What is UUID Generator?

How It Works

How to Use

Who Uses This Tool

Why Choose This Tool

Key Benefits

Frequently Asked Questions

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