Which UUID version does this tool generate?

It generates version 4 UUIDs, which are almost entirely random. Version 4 is the most common general-purpose choice because it needs no timestamp, MAC address, or coordination — every value is independently random, making it ideal for identifiers created on many machines at once.

Are these UUIDs cryptographically secure?

Yes. The tool uses the browser's crypto.randomUUID function, which is backed by a cryptographically secure random number generator. That means the values are not predictable from one another, unlike identifiers built on Math.random, which should never be used where unpredictability matters.

Can two version 4 UUIDs ever collide?

It is theoretically possible but practically negligible. With 122 random bits there are about 5 times 10^36 possibilities. You would have to generate billions of UUIDs every second for decades before the odds of even a single collision became meaningful, so for virtually any real application they can be treated as unique.

What is the difference between v1, v4, and v7?

Version 1 encodes a timestamp and MAC address, making it time-sortable but potentially identifying. Version 4 is fully random with no ordering. Version 7 combines a millisecond timestamp in its leading bits with random bits, giving both uniqueness and time ordering, which is increasingly preferred for database keys because sequential values index efficiently.

Why might a random v4 UUID be a poor database primary key?

Because v4 values have no order, inserting them into a clustered or B-tree index scatters writes across the index, causing page splits and fragmentation that slow inserts on large tables. Time-ordered identifiers like UUID v7 or an auto-increment column avoid that by keeping new rows at the end of the index.

Is a UUID the same thing as a GUID?

Yes. GUID (Globally Unique Identifier) is the term Microsoft uses, while UUID is the term from the formal standard. They describe the same 128-bit identifier format, and the two names are interchangeable in practice.

Is anything sent to a server when I generate a UUID?

No. UUIDs are produced entirely in your browser by the native crypto API. No request is made and no value is logged, so the identifiers you generate stay completely local to your device.

Developer Tools

UUID Generator — Free v4 UUIDs, No Server Required

🔒 Runs in your browser

Generate cryptographically secure v4 UUIDs using your browser's built-in CSPRNG (crypto.randomUUID). No server, no logs — UUIDs are generated and stay entirely local. Copy any UUID in one click.

How to use this tool

Click Generate to produce a cryptographically secure v4 UUID.
Generate as many as needed — each is unique.
Click any UUID to copy it to your clipboard.

Count:

About UUID Generator

A UUID (Universally Unique Identifier), also called a GUID, is a 128-bit value written as 32 hexadecimal digits in the familiar 8-4-4-4-12 grouping, for example 550e8400-e29b-41d4-a716-446655440000. Its purpose is to let independent systems mint identifiers that are practically guaranteed not to collide, without any central coordinator handing out numbers. That makes UUIDs the standard choice for primary keys generated on the client, message and event IDs in distributed systems, idempotency keys, and file or resource names that must be unique across machines.

There are several versions defined by the standard. Version 1 embeds a timestamp and the machine's MAC address, which makes it sortable by creation time but can leak hardware identity. Version 4 is fully random — 122 of its 128 bits come from a random source, with the rest fixed to mark the version and variant. Version 7, a more recent addition, places a Unix millisecond timestamp in the high bits followed by random bits, giving you the collision resistance of v4 while remaining time-ordered, which is valuable as a database key because sequential inserts keep index pages from fragmenting.

This tool generates version 4 UUIDs using the browser's built-in crypto.randomUUID function, which draws from a cryptographically secure random number generator (CSPRNG) rather than the predictable Math.random. That distinction matters: a CSPRNG produces values that cannot be guessed even by an attacker who has seen prior outputs. You can generate a single UUID or a batch of up to 25 at once and copy any of them, or all of them, with one click.

The often-asked question is whether v4 UUIDs can collide. In principle yes; in practice the probability is so small it can be ignored. With 122 random bits there are roughly 5 times 10^36 possible values, and you would need to generate on the order of a billion UUIDs per second for about 85 years before the chance of a single duplicate reached even fifty percent. The trade-off to be aware of is that random v4 values are not sortable and, used as a clustered database key, can hurt insert performance compared to sequential or time-ordered IDs — which is precisely the gap v7 was designed to close. Generation here is entirely local; nothing is sent anywhere.

Frequently Asked Questions

Which UUID version does this tool generate?: It generates version 4 UUIDs, which are almost entirely random. Version 4 is the most common general-purpose choice because it needs no timestamp, MAC address, or coordination — every value is independently random, making it ideal for identifiers created on many machines at once.
Are these UUIDs cryptographically secure?: Yes. The tool uses the browser's crypto.randomUUID function, which is backed by a cryptographically secure random number generator. That means the values are not predictable from one another, unlike identifiers built on Math.random, which should never be used where unpredictability matters.
Can two version 4 UUIDs ever collide?: It is theoretically possible but practically negligible. With 122 random bits there are about 5 times 10^36 possibilities. You would have to generate billions of UUIDs every second for decades before the odds of even a single collision became meaningful, so for virtually any real application they can be treated as unique.
What is the difference between v1, v4, and v7?: Version 1 encodes a timestamp and MAC address, making it time-sortable but potentially identifying. Version 4 is fully random with no ordering. Version 7 combines a millisecond timestamp in its leading bits with random bits, giving both uniqueness and time ordering, which is increasingly preferred for database keys because sequential values index efficiently.
Why might a random v4 UUID be a poor database primary key?: Because v4 values have no order, inserting them into a clustered or B-tree index scatters writes across the index, causing page splits and fragmentation that slow inserts on large tables. Time-ordered identifiers like UUID v7 or an auto-increment column avoid that by keeping new rows at the end of the index.
Is a UUID the same thing as a GUID?: Yes. GUID (Globally Unique Identifier) is the term Microsoft uses, while UUID is the term from the formal standard. They describe the same 128-bit identifier format, and the two names are interchangeable in practice.
Is anything sent to a server when I generate a UUID?: No. UUIDs are produced entirely in your browser by the native crypto API. No request is made and no value is logged, so the identifiers you generate stay completely local to your device.

Embed this tool on your site

Free. One line of HTML — the tool runs in your visitor's browser, no data sent to anyone.

<iframe src="https://brevio.pro/embed/uuid-generator" width="100%" height="600" loading="lazy" style="border:1px solid #e5e5e5;border-radius:8px" title="UUID Generator — brevio"></iframe>
<p style="font:12px/1.4 sans-serif"><a href="https://brevio.pro/tools/uuid-generator">UUID Generator</a> by <a href="https://brevio.pro">brevio</a></p>

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