UUID Generator
Generate cryptographically random version 4 UUIDs singly or in bulk up to 500, in upper or lower case. Free, no sign-up, and it runs in your browser.
Dedicated page: /en/uuid-generator
Quick answer
A UUID generator creates universally unique identifiers: 128-bit values shown as 32 hex digits in five groups, like 550e8400-e29b-41d4-a716-446655440000. This tool generates version 4 UUIDs, randomly created, one at a time or in bulk, in upper or lower case, with or without hyphens.
About this UUID Generator
Generate cryptographically random version 4 UUIDs singly or in bulk up to 500, in upper or lower case. It is one of the Developer Tools on ToolUstad, and like every tool here it runs entirely in your browser: nothing you type, paste or open is uploaded to a server, and there is no sign-up or usage limit.
What is a UUID?
A UUID, universally unique identifier, also called a GUID in Microsoft systems, is a 128-bit identifier designed to be unique without any central registry. The standard text form groups the hex digits 8-4-4-4-12. Version 4 UUIDs are generated from random numbers: 122 of the 128 bits are random, and the remaining bits mark the version and variant. The chance of a collision is so small that developers treat generated UUIDs as unique in practice.
Where UUIDs are used
- Database primary keys: especially in distributed systems that cannot coordinate auto-increment IDs.
- API resources: order, user and session identifiers that do not leak how many records exist.
- File and object storage: upload names that never clash between users.
- Transactions and idempotency keys: safe retries without double processing.
- Testing: realistic unique seed data in bulk.
UUID versions, briefly
| Version | Based on | Typical use |
|---|---|---|
| v1 | Time plus device MAC address | Legacy systems; leaks creation time |
| v3 / v5 | Hash of a name (MD5 / SHA-1) | Reproducible IDs for the same input |
| v4 | Random numbers | The general default; what this tool makes |
| v7 | Time ordered plus randomness | Newer databases that want sortable IDs |
Best practices
- Generate UUIDs with a cryptographically secure random source, as this tool does via the browser crypto API.
- Store them in a native UUID or binary(16) column rather than text where your database supports it.
- Keep one canonical format, lowercase with hyphens, across your whole system.
Common mistakes to avoid
- Using a weak random generator or Math.random for IDs that must be unguessable.
- Assuming sequential IDs are fine for public URLs: they reveal record counts and invite guessing.
- Mixing uppercase and lowercase forms and then failing string comparisons.
Who is the UUID generator for?
Developers, database administrators, QA engineers building test data, and anyone who needs a handful of unique IDs right now. Every language has a UUID library, but spinning up a project or a REPL just to print ten IDs is overkill when a browser tab does it instantly, in bulk, in the exact format you need.
How random is random enough?
A version 4 UUID is only as good as the randomness behind it. Weak generators that seed from the clock or use a non cryptographic pseudo random function can produce predictable or repeating IDs, which is why this tool draws exclusively on the browser's crypto.getRandomValues interface, the same entropy source browsers use for security operations. In practice the numbers are indistinguishable from true random for ID generation.
UUIDs as database keys: the honest trade off
UUID primary keys solve real problems: records can be created offline or on many servers without coordination, IDs can be safely shown in URLs, and merging databases never collides. The costs are also real: 16 byte keys are bigger than 8 byte integers, and random insertion order fragments clustered indexes, which is why time ordered v7 UUIDs are gaining ground for new systems. Knowing that trade off, and testing with bulk generated IDs like the batches from this page, beats discovering it in production.
For fixtures and load tests, generate a few hundred v4 UUIDs here, paste them into your seed script, and your test data will behave like production data instead of the suspiciously tidy 1, 2, 3 of hand written fixtures.
Learn: how to use the UUID Generator
- Copy the single UUID at the top with one click, or set a bulk quantity.
- Choose lowercase or UPPERCASE and whether to keep hyphens.
- Click Generate UUIDs, then copy all or download the list.
Features
- True version 4 UUIDs from your browser's secure random generator
- Bulk generation of 1 to 500 UUIDs
- Uppercase or lowercase, hyphens on or off
- One-click copy for the single UUID, copy-all and download for bulk
Worked example
f47ac10b-58cc-4372-a567-0e02b2c3d479 is a valid v4 UUID: the 13th character is always 4 and the 17th is always 8, 9, a or b. This tool produces that format every time.
Frequently asked questions
What is a version 4 UUID?
A UUID is a 128-bit identifier written as 32 hex digits in five groups. Version 4 means it is generated from random numbers, so no central registry is needed.
Can two generated UUIDs ever collide?
In practice, no. There are about 5.3 x 10^36 possible v4 UUIDs. You would need to generate billions per second for centuries before a collision became likely.
Where are UUIDs used?
Database primary keys, API request IDs, file names, session tokens and anywhere systems need unique IDs without coordinating.
Are the UUIDs generated on a server?
No. They are created in your browser using the Web Crypto API.
Can two version 4 UUIDs ever be identical?
In theory yes, in practice almost never. With 122 random bits there are about 5.3 x 10^36 possible values; you would need to generate billions per second for decades before a collision became likely.
What is the difference between a UUID and a GUID?
They are the same concept. GUID is Microsoft's name for its implementation of the UUID standard. A GUID generated on Windows and a UUID generated here follow the same format and can be used interchangeably.
How many UUIDs can I generate at once?
This tool generates bulk batches up to 1,000 at a time, each on its own line, ready to copy into seed scripts, spreadsheets or test fixtures.
Are UUIDs case sensitive, and does format matter?
The specification treats the hex digits case insensitively, and most systems accept upper or lower case. In practice, pick one format and stay consistent: string comparisons in code and databases may be case sensitive even when the standard is not, and mixed formats are a classic source of 'record not found' bugs during data imports.
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