Is a UUID v4 guaranteed to be unique?

No. RFC 9562 says global uniqueness cannot be guaranteed without a shared scheme, and a v4 value is only 122 random bits. A repeat is very unlikely, but a table that must never hold two equal keys should still enforce that with a unique constraint.

Is a GUID the same as a UUID?

Yes. RFC 9562 names GUID (Globally Unique IDentifier) as another name for a UUID, and GUID is the term Microsoft uses. A v4 UUID from this page works wherever a GUID is asked for. It is printed in lower case without braces; some tools write the same value in upper case or inside { }.

Can I use a UUID as a password reset token or API key?

Not on its own. RFC 9562 says implementations should not assume UUIDs are hard to guess and must not use them as security capabilities, identifiers whose mere possession grants access. Use a token generator built for secrets instead.

How many UUIDs can I generate at once?

From 1 to 1,000 whole numbers. Empty, 0, 1001, 2.5, -3 and 1e3 each show a message next to the field, and Generate stays off until the number is valid.

How do I make a version 5 UUID from a name?

Choose Version 5, pick the namespace (DNS, URL, OID or X.500 from RFC 9562, or a custom UUID) and type the name. The namespace and the name, in UTF-8, are hashed with SHA-1, so the same pair always gives the same UUID: DNS and www.example.com give 2ed6657d-e927-568b-95e1-2665a8aea6a2, and version 3, which uses MD5, gives 5df41881-3aed-3515-88a7-2f4a814cf09e. Those are the test values in RFC 9562 appendix A. Anyone who guesses the name can compute the UUID, so it is not a secret.

What is the difference between UUID v4 and UUID v7?

A v4 value is random, so new values land at scattered positions in a database index (RFC 9562 section 2.1). A v7 value starts with a millisecond timestamp, so its text form sorts in time order. The UUID v7 Generator makes and decodes those.

UUID Generator

Generate 1 to 1,000 random v4 UUIDs, or time-based v1, or name-based v5 and v3 from a namespace and a name, and copy them. Repeats of v4 are very unlikely. How it works

Version

Random: 122 bits from the browser's cryptographic generator. For IDs that sort by time, use the UUID v7 generator.

Quantity

About the UUID Generator

A version 4 UUID has 122 random bits, written as 32 hex digits in 8-4-4-4-12 groups, such as 550e8400-e29b-41d4-a716-446655440000. This generator makes 1 to 1,000 of them from the browser’s cryptographic random source and copies the list. Repeats are possible but very unlikely, as the example below works out. The Version list also makes time-based version 1 UUIDs and name-based versions 5 and 3: the DNS namespace and the name www.example.com always give the version 5 UUID 2ed6657d-e927-568b-95e1-2665a8aea6a2.

How to use this tool

Choose the Version: 4 (random, the default), 1 (time-based), or 5 or 3 (name-based).
For version 4 or 1, type a quantity from 1 to 1,000 and press Generate; the list on screen is replaced. For version 5 or 3, pick the namespace and type the name.
Press Copy for the whole list, one UUID per line, or the copy button on a row for one UUID.

Frequently asked questions

Is a UUID v4 guaranteed to be unique?: No. RFC 9562 says global uniqueness cannot be guaranteed without a shared scheme, and a v4 value is only 122 random bits. A repeat is very unlikely, but a table that must never hold two equal keys should still enforce that with a unique constraint.
Is a GUID the same as a UUID?: Yes. RFC 9562 names GUID (Globally Unique IDentifier) as another name for a UUID, and GUID is the term Microsoft uses. A v4 UUID from this page works wherever a GUID is asked for. It is printed in lower case without braces; some tools write the same value in upper case or inside { }.
Can I use a UUID as a password reset token or API key?: Not on its own. RFC 9562 says implementations should not assume UUIDs are hard to guess and must not use them as security capabilities, identifiers whose mere possession grants access. Use a token generator built for secrets instead.
How many UUIDs can I generate at once?: From 1 to 1,000 whole numbers. Empty, 0, 1001, 2.5, -3 and 1e3 each show a message next to the field, and Generate stays off until the number is valid.
How do I make a version 5 UUID from a name?: Choose Version 5, pick the namespace (DNS, URL, OID or X.500 from RFC 9562, or a custom UUID) and type the name. The namespace and the name, in UTF-8, are hashed with SHA-1, so the same pair always gives the same UUID: DNS and www.example.com give 2ed6657d-e927-568b-95e1-2665a8aea6a2, and version 3, which uses MD5, gives 5df41881-3aed-3515-88a7-2f4a814cf09e. Those are the test values in RFC 9562 appendix A. Anyone who guesses the name can compute the UUID, so it is not a secret.
What is the difference between UUID v4 and UUID v7?: A v4 value is random, so new values land at scattered positions in a database index (RFC 9562 section 2.1). A v7 value starts with a millisecond timestamp, so its text form sorts in time order. The UUID v7 Generator makes and decodes those.

Where random UUIDs are used

Make identifiers for database rows, test data, file names, idempotency keys or session records without asking a central service for the next number. Set a quantity from 1 to 1,000 and press Generate: the list on screen is what Copy copies, one UUID per line, and each row has its own copy button. The UUIDs are lower-case values in 8-4-4-4-12 form, the same values Microsoft software calls GUIDs.

The Version list adds version 1 (time-based) and the name-based versions 5 and 3. A name-based UUID is the same every time for the same namespace and name. For IDs that sort by time, use the UUID v7 Generator.

How a v4 UUID is made

128 bits − 4 version bits − 2 variant bits = 122 random bits, so there are 2^122, about 5.3 × 10^36, possible v4 values (RFC 9562 section 5.4). The tool uses crypto.randomUUID when the browser has it and crypto.getRandomValues otherwise, which also works on plain http pages where randomUUID does not. If neither exists it says so and makes nothing; there is no fallback to Math.random.

Every value has the shape xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx: the 4 is the version and y is 8, 9, a or b, the two variant bits. For example, 550e8400-e29b-41d4-a716-446655440000 has version 4 and variant a.

Repeats are very unlikely but not impossible: RFC 9562 section 6.8 says global uniqueness cannot be guaranteed without a shared scheme. By the usual birthday approximation, n ≈ 1.1774 × √(2^122) values, about 2.7 × 10^18, give a 50% chance of one repeat.

Versions 5 and 3 hash the namespace UUID followed by the name in UTF-8, with SHA-1 for 5 and MD5 for 3, then set the version and variant bits. The DNS namespace and www.example.com, the page's default, give v5 2ed6657d-e927-568b-95e1-2665a8aea6a2 and v3 5df41881-3aed-3515-88a7-2f4a814cf09e, the test values in RFC 9562 appendix A. Version 1 counts 100-nanosecond steps since 15 October 1582 and ends in a random node ID with the multicast bit set (section 6.10), so no device address is written.

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