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UUID/GUID Generator

Developer Tools

Generate RFC 4122 version 4 UUIDs (GUIDs) instantly for development and testing. Create one or many at once, copy with a single click, no sign-up required.

Reviewed by the thecalcu.com team · Last updated June 17, 2026

What is a UUID?

A UUID/GUID Generator produces Universally Unique Identifiers, 128-bit values written as 32 hexadecimal characters in the standard 8-4-4-4-12 hyphenated format, such as f47ac10b-58cc-4372-a567-0e02b2c3d479. UUIDs let independent systems generate unique identifiers without any coordination or central registry, which is exactly why they're the default choice for database primary keys, API resource IDs, and distributed-system trace IDs across modern software.

This tool generates version 4 UUIDs specifically, the most common variant, built almost entirely from cryptographically random bits rather than from a timestamp or hardware address. For developers who need a quick, reliable identifier without spinning up a database or writing a script, the UUID Generator produces one (or several at once) in your browser instantly. Pair it with the Password Generator when you need a secret credential rather than a unique, non-secret identifier.

Why Use a UUID Generator?

Writing a one-off script just to generate a test UUID is a waste of a developer's time, and copying an example UUID from documentation risks an accidental collision if you forget to change it before using it in real data. This tool generates a fresh, guaranteed-unique-in-practice UUID in the time it takes to load a page, no terminal, no script, no dependency to install.

It's especially useful when seeding test databases, writing fixture data for automated tests, or quickly creating a placeholder ID while prototyping an API response, where you need several distinct, realistic-looking UUIDs without writing any code at all.

Who Should Use This Generator?

Backend developers use UUID generators constantly when seeding databases, writing migration scripts, or testing how their application handles primary keys. QA engineers generate batches of UUIDs to populate test fixtures with unique, non-colliding record IDs. API developers use them as request or trace identifiers when documenting example payloads. Students and bootcamp learners working through database or backend tutorials often need a quick UUID without installing a UUID library just to follow along.

If your goal is a unique secret rather than a unique identifier, the Password Generator is the right tool, a UUID is not designed to be kept private the way a password is.

What Insights Does the UUID Generator Give You?

Each generated value is a complete, standards-compliant version 4 UUID, there's no "quality" spectrum to interpret the way there is with password strength, since every version 4 UUID drawn from a proper random source is equally valid and equally unlikely to collide. The two format toggles (uppercase, hyphens) exist purely to match whatever convention your target system expects, not to change the underlying randomness or uniqueness guarantee.

Generating multiple UUIDs at once is useful for seeing the format consistency across a batch, every value will share the same 4 in the third group and the same 8/9/A/B leading character in the fourth group, which is a quick way to sanity-check that a script or system you're integrating with is producing valid version 4 UUIDs too.

How to use this UUID calculator

  1. Set the Number of UUIDs field to how many you need, from 1 up to 20 at a time.
  2. Toggle Uppercase on if your target system expects uppercase hexadecimal characters (most do not).
  3. Toggle Include Hyphens off if your target system stores UUIDs without separators.
  4. Review the generated UUID(s) in the result box, each one appears on its own line.
  5. Click the copy icon to copy all generated UUIDs to your clipboard, then paste them into your database, script, or test fixture file.

Formula & Methodology

A version 4 UUID is a 128-bit value where 6 bits are fixed to mark the format and the remaining 122 bits are random:

- The third group always starts with 4, marking the UUID version.
- The fourth group always starts with 8, 9, A, or B, marking the UUID variant (RFC 4122).
- The other 122 bits are filled using your browser's cryptographically secure random number generator (crypto.randomUUID(), or a manual fallback built on crypto.getRandomValues()).

This gives 2^122 ≈ 5.3 × 10^36 possible values per generation. The well-known "practically zero collision risk" claim comes from the birthday-paradox calculation: even generating 1 billion UUIDs per second continuously, it would take roughly 85 years before there is just a 50% probability that any two of them ever collide, far beyond any realistic usage on this platform.

Frequently Asked Questions

A UUID (Universally Unique Identifier), also called a GUID (Globally Unique Identifier), is a 128-bit value used to uniquely identify information without needing a central authority to coordinate the assignment. UUIDs are written as 32 hexadecimal characters grouped into five sections separated by hyphens, like `f47ac10b-58cc-4372-a567-0e02b2c3d479`.
This tool generates version 4 UUIDs, which are built almost entirely from random bits drawn using your browser's `crypto.randomUUID()` API (or a manual fallback using `crypto.getRandomValues()` if that API is unavailable). Only 6 of the 128 bits are fixed to mark the version and variant, the remaining 122 bits are cryptographically random.
A standard UUID is written as `xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx`, 32 hexadecimal digits in groups of 8-4-4-4-12, separated by hyphens. The `4` in the third group marks it as version 4, and the first character of the fourth group (`y`) is always 8, 9, A, or B, marking the variant.
Set the **Number of UUIDs** field to however many you need at once, optionally toggle uppercase or remove hyphens to match your system's expected format, and the result updates instantly. Click the copy icon to copy all generated UUIDs to your clipboard at once.
Set the count field to any number from 1 to 20 and the tool generates that many unique UUIDs in one go, each on its own line in the result box, ready to paste into a spreadsheet, seed script, or test fixture file.
Yes, generation happens entirely inside your browser using the Web Crypto API, and nothing is sent to a server, logged, or stored. UUIDs are not secrets in the way passwords are, but the same client-side, zero-transmission design applies here too.
It is mathematically possible but practically impossible to worry about. Version 4 UUIDs have 122 random bits, giving roughly 2.7 × 10^38 possible values, even generating a billion UUIDs a second, you would need to run for longer than the age of the universe before a 50% chance of any collision occurring.
There is no functional difference for everyday use, GUID is simply Microsoft's term for the same 128-bit identifier concept that the rest of the industry calls a UUID, and both follow the same RFC 4122 format. This tool generates standard RFC 4122 version 4 UUIDs, which are accepted anywhere a GUID is expected.
Most systems expect the standard hyphenated format (`8-4-4-4-12`), but some databases and APIs store UUIDs without hyphens to save space. Use the **Include Hyphens** toggle to switch between the two formats depending on what your target system expects.
Most systems are case-insensitive for UUIDs, but a few legacy systems or specific column formats expect uppercase hexadecimal characters. Toggle **Uppercase** on if your target system documentation specifically calls for it.
UUIDs are used as primary keys in databases, as unique request/trace IDs in distributed systems and logging, as identifiers for files and API resources, and anywhere multiple systems need to generate unique IDs independently without checking with each other first. If you need a memorable secret rather than a unique identifier, use the [Password Generator](/password-generator/) instead.
Yes, once the page has loaded, UUID generation runs entirely in your browser with no further network requests, so it keeps working even offline.
Also known as
GUID generatorUUID v4unique ID generatorrandom UUIDGUID creatoruniversally unique identifier