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UUID Generator (GUID)

A bulk UUID generator: create 1 to 100 version 4 UUIDs per click from your browser's cryptographic random generator, formatted lowercase, uppercase, without hyphens, or in braces for Windows and .NET GUIDs.

Mode Count

UUID v4 uses browser cryptographic randomness. Time-based v1 identifiers are intentionally not offered.

Result

How a version 4 UUID is built

Size128 bits = 32 hex digits, written 8-4-4-4-12 with hyphens (36 characters)
Fixed bits4 version bits (0100 → "4") + 2 variant bits (10 → 8, 9, a or b)
Random bits128 − 6 = 122 bits from a cryptographically secure generator
Possible values2^122 ≈ 5.32e+36

The generator calls your browser's crypto.randomUUID(), which draws from the same secure random source used for encryption keys. It makes 1 to 100 UUIDs per click, one per line, then applies the format you pick. Formats don't change the value — only how it's written.

UUID v4 uses browser cryptographic randomness. Time-based v1 identifiers are intentionally not offered.

Worked example

One UUID generated when this page was built, split into its five groups:

343e5986-3ad3-4084-9ada-50cc1fa2d774

The third group starts with 4 (the version) and the fourth with 9 (the variant). Everything else is random.

Format	Output	Chars
Lowercase	343e5986-3ad3-4084-9ada-50cc1fa2d774	36
Uppercase	343E5986-3AD3-4084-9ADA-50CC1FA2D774	36
No hyphens	343e59863ad340849ada50cc1fa2d774	32
Braces	{343e5986-3ad3-4084-9ada-50cc1fa2d774}	38

Lowercase is the standard form: RFC 9562 says UUIDs should be output in lowercase and accepted in either case. Use uppercase or braces only where a tool expects them, such as Windows registry keys or .NET's "B" format.

How likely is a duplicate?

The birthday approximation gives the chance that any two of n random UUIDs match:

p ≈ 1 − e^(−n² ÷ (2 × 2^122))

UUIDs generated	Chance of any duplicate
1,000,000	9.4e-26
1,000,000,000	9.4e-20
1,000,000,000,000	9.4e-14
2.71e+18	0.5

What actually causes duplicates

Real collisions come from bugs, not chance: a random generator seeded the same way on cloned virtual machines, a non-cryptographic Math.random() implementation, or code that copies one ID into several records. Still put a unique constraint on UUID columns so a bug fails loudly instead of merging data.

Uniqueness is not secrecy. A UUID in a URL is fine as an identifier, but don't rely on it being unguessable — check permissions on every request.

UUID versions at a glance

Version	Built from	Notes
v1	Timestamp + node ID (often the MAC address)	Leaks time and machine; superseded by v6/v7
v3	MD5 hash of a namespace + name	Same input always gives the same UUID
v4	122 random bits	This tool. No meaning, nothing leaked
v5	SHA-1 hash of a namespace + name	Preferred over v3 for name-based IDs
v6	v1 fields reordered so they sort by time	For systems already using v1
v7	Unix time in milliseconds + random bits	Sorts by creation time; good for database keys
v8	Custom, vendor-defined layout	For experimental or special uses

Pick v4 when you just need an ID nobody else will produce. Pick v7 when IDs are database keys and you want new rows to land near each other in the index. Pick v5 when the same input — a URL or an email address in a namespace — must always map to the same UUID. The special nil UUID is all zeros and the max UUID is all f's.

Sources: RFC 9562, "Universally Unique IDentifiers (UUIDs)" (IETF, May 2024, obsoletes RFC 4122); W3C Web Cryptography API, Crypto.randomUUID(). Checked 15 October 2026.

Frequently asked questions

What is the difference between a UUID and a GUID?+

Nothing technical. GUID (globally unique identifier) is Microsoft's name for the same 128-bit identifier the standards call a UUID. Windows tools often show GUIDs in uppercase or inside braces, which is why the generator offers those formats.

Can two random UUIDs ever be the same?+

In theory yes, in practice no. A version 4 UUID has 122 random bits. You would need to generate about 2.71 quintillion of them before the chance of any duplicate reached 50% — around 86 years at a billion UUIDs per second. A flawed random source is a far bigger risk than the math, which is why this tool uses the browser's cryptographic generator.

How do I generate many UUIDs at once?+

Set Count to any whole number from 1 to 100 and press Generate / convert. Each UUID goes on its own line, ready to copy or download as a text file. Need more? Press the button again and append the next batch — every one is generated independently.

How can I tell a UUID is version 4?+

Look at the first character of the third group: it is always 4. The first character of the fourth group is 8, 9, a or b, which marks the standard variant. For example, in xxxxxxxx-xxxx-4xxx-axxx-xxxxxxxxxxxx the 4 and the a are fixed by the format; the other 30 hex digits are random.

Why doesn't it offer UUID v1 or v7?+

Version 1 embeds a timestamp and often the machine's MAC address, which leaks when and where an ID was made, so it is intentionally left out. Version 7 (time-ordered) is not generated here either; if you need IDs that sort by creation time, generate v7 in your application with a library that implements RFC 9562.

Should I use UUIDs as database primary keys?+

They work well when IDs must be created on many machines without coordination, or must not reveal how many records exist. The trade-off: v4 values are random, so inserts land all over a B-tree index, and they take 16 bytes (36 as text) versus 4 or 8 for an integer. Store them in a native UUID type where your database has one.

Can I use a UUID as a secret token or password reset link?+

It isn't recommended. RFC 9562 warns not to assume UUIDs are hard to guess. A v4 UUID from crypto.randomUUID() does carry 122 random bits, but many systems create UUIDs with weaker generators. For session or reset tokens, use a purpose-built random token instead.

How long is a UUID?+

A UUID is 128 bits, written as 32 hexadecimal digits. The standard form groups them 8-4-4-4-12 with hyphens, for 36 characters in all; the no-hyphen option gives 32 characters, and the braces option adds { and } for 38.

Are UUIDs case-sensitive?+

No. RFC 9562 says UUIDs should be written in lowercase but compared without regard to case, so 3F2504E0-… and 3f2504e0-… are the same identifier. Some systems store them as plain text, though, so pick one case and use it consistently.

How do I generate a UUID in code?+

In browsers and Node.js, call crypto.randomUUID() (browsers allow it only on secure pages, such as HTTPS or localhost). In Python use uuid.uuid4(); in PostgreSQL 13 and later, gen_random_uuid(); in SQL Server, NEWID(). All of these produce random version 4 UUIDs like the ones here.

Are the UUIDs I generate stored or logged?+

No. They are created by your browser's crypto.randomUUID() function on your device. Nothing is sent to a server or kept after you leave the page, so no one else has a copy of your list.