UUID Generator
Generate random version 4 UUIDs, also called GUIDs, one at a time or up to 100 at once. They come from your browser's cryptographically secure random generator, and you can switch to uppercase or drop the hyphens before copying one or all of them. Free, no sign-up, and nothing is sent to a server.
How to Use the UUID Generator
- 1. Choose how many. Any whole number from 1 to 100; the default is 5.
- 2. Press Generate. A new list appears each time. Nothing is generated until you press the button.
- 3. Pick the format. Uppercase and No hyphens reformat the list you already have; they do not generate new values.
- 4. Copy. Each row has its own Copy button, and Copy All copies the whole list, one UUID per line.
Anatomy of a Version 4 UUID
A UUID is a 128-bit identifier, written as 32 hexadecimal digits in five groups separated by hyphens — 8-4-4-4-12 — which makes 36 characters. The format is defined in RFC 9562 (2024), which replaced RFC 4122. Version 4 fills almost all of the bits with random data; only six are fixed:
| Part | Where | Value |
|---|---|---|
| Version | First digit of the third group | Always 4 |
| Variant | First digit of the fourth group | One of 8, 9, a or b |
| Random bits | Everything else | 122 bits |
A sample, as the tool's randomness produces it: e1f22e6e-ea3f-42a7-b43d-164b51542675. The third group begins with 4 and the fourth with b, as every v4 UUID must. Yours will differ; that is the point.
Will Two UUIDs Ever Collide?
With 122 random bits there are 2122 possible values, about 5.3 × 1036. By the birthday bound, you would need roughly 2.7 × 1018 UUIDs for even a 50% chance that any two match. Generating a billion a second, that takes about 86 years. For ordinary applications — database keys, request IDs, filenames — collisions are not a practical concern, provided the random source is good. This tool uses the browser's cryptographic generator (crypto.randomUUID, with a crypto.getRandomValues fallback), not Math.random.
Which UUID Version Do You Need?
| Version | Built from | Typical use |
|---|---|---|
| 1 | Clock time (Gregorian) and a node identifier | Legacy systems; it can expose when and where it was made |
| 3 and 5 | A hash (MD5 or SHA-1) of a namespace and a name | Stable IDs derived from a name |
| 4 | Random bits | General-purpose unique IDs — what this tool makes |
| 7 | Unix millisecond timestamp, then random bits | Database keys that sort by creation time |
RFC 9562 notes that v4's randomness gives poor locality in database indexes and recommends version 7 over versions 1 and 6 for time-based IDs. If your table is large and inserts are frequent, a time-ordered v7 may suit it better than v4. This page generates v4 only. The RFC also says UUIDs should be stored in a database as 16-byte binary where possible, since text takes 36 characters.
Formats: Hyphens, Case and GUIDs
RFC 9562 allows hex digits in upper, lower or mixed case, and the same UUID in either case is the same identifier. The standard text form has hyphens; the 32-digit form without them is a common variation that many databases and APIs accept, but check yours before using it. GUID is Microsoft's name for the same 128-bit identifier, so a v4 UUID from this page works wherever a GUID is expected.
Frequently Asked Questions
- What is a UUID v4?
- A universally unique identifier of 128 bits in which 122 bits are random and six mark the version (4) and variant. It is written like 550e8400-e29b-41d4-a716-446655440000.
- Can two generated UUIDs collide?
- In theory yes; in practice no. There are about 5.3 × 1036 possible values, and a 50% chance of any collision needs roughly 2.7 × 1018 UUIDs, about 86 years at a billion per second.
- Is the randomness cryptographically secure?
- Yes. The tool calls the browser's crypto.randomUUID, or crypto.getRandomValues where that is missing, both of which use a cryptographically secure random number generator rather than Math.random.
- Are the UUIDs generated on a server?
- No. They are made in your browser, are not sent anywhere, and are not stored. Generating again gives a completely new list.
- Is a UUID the same as a GUID?
- Yes. GUID is Microsoft's term for the same 128-bit identifier. A version 4 UUID can be used as a GUID without change; Windows tools sometimes show GUIDs in uppercase or inside braces.
- What do Uppercase and No hyphens do?
- They change only how each value is written. Uppercase turns the hex letters into capitals, which RFC 9562 treats as the same UUID. No hyphens removes the dashes to give 32 characters; use it only where the receiving system expects that form.
- Can I use a UUID as a secret or password?
- No. A UUID is designed to be unique, not secret. RFC 9562 says implementations should not assume UUIDs are hard to guess and must not use them as security capabilities. Use the Password Generator for secrets.