UUID Format
Lowercase UUID Generator
Lowercase hex is what RFC 4122 and RFC 9562 use in every example, and what most databases, languages and libraries emit by default.
Canonical RFC formAny versionDefault everywhere
Generated locally with the Web Crypto API — nothing leaves your browser.
What Is Lowercase UUID Generator?
- The RFCs present UUIDs in lowercase, so this is the form you will see from
crypto.randomUUID(), Python'suuid4(), and PostgreSQL'sgen_random_uuid(). - Sticking to lowercase end-to-end avoids the small class of bugs where two services store the same identifier in different cases and a string comparison fails.
How to generate
- Leave the Uppercase toggle off.
- Choose your version and generate.
- Copy the lowercase value.
Use Cases
- API responses that follow the RFC's presentation.
- Cross-language systems where normalisation must be predictable.
- URL path segments, which are conventionally lowercase for consistency.
How Lowercase UUID Generator Compares
| Lowercase (canonical) | 9a8b7c6d-5e4f-4a3b-8c1d-2e3f4a5b6c7d |
| Uppercase | 9A8B7C6D-5E4F-4A3B-8C1D-2E3F4A5B6C7D |
| Mixed | Avoid — hardest to compare reliably |
Code Examples
JavaScript
const id = crypto.randomUUID(); // already lowercasePython
import uuid
print(str(uuid.uuid4())) # lowercaseFrequently Asked Questions
Is lowercase required by the standard?
The RFCs use lowercase in examples; they do not mandate it. Following the examples avoids surprises.
Why did my API return uppercase?
Usually a database column default or an ORM formatter. Normalise once at the boundary.
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