# UUID v4 Generator

- **URL:** https://codeasystem.com/calculators/developer/uuid-generator/
- **Category:** developer
- **Description:** Generate one to fifty random UUID version-4 identifiers using crypto.randomUUID with a documented RFC 4122 fallback.
- **Primary output:** Generated UUIDs (v4): 5 random UUIDs, lowercase

## Inputs
- How many (name: `count`, type: number, example: 5)
- Letter case (name: `uppercase`, type: select)

## Outputs
- Generated UUIDs (v4): 5 random UUIDs, lowercase
- All UUIDs (newline-separated): ddf86689-8503-45cf-88b9-6676ef39b72a
ad240693-7c78-4ff6-afd5-ceb46b9961a2
eda8c72d-9a28-402d-b42d-d88f2bf6b350
78731aba-1638-4300-ba2f-01557993f083
85cc366e-afb5-4978-bc0f-c3ff2202f33a
- Version / variant bits: version 4, RFC 4122 variant (10xx)
- Uniqueness check on this batch: 5 of 5 distinct

## Formula / methodology
```
122 random bits → hex 8-4-4-4-12 with version nibble 4 and variant bits 10xx
```

Each identifier draws randomness from crypto.randomUUID() where the platform provides it, falling back to sixteen cryptographically-filled bytes with the RFC 4122 version-4 and variant bits set manually; identical guarantees either way.

The batch is checked internally for duplicates as a sanity signal. Generation happens at runtime, so the primary summary stays deterministic while the fresh UUIDs appear in the rows below, ready to copy.

## Assumptions & limitations
- Randomness comes from the platform CSPRNG (or Math.random fallback in insecure contexts).
- Version field fixed at 4; variant fixed at RFC 4122 (10xx).
- Batches capped at 50 per run.

## How to use
1. **Set the count**; Anywhere from one test fixture to a bulk list of fifty.
2. **Choose letter case**; Databases rarely care; some legacy systems insist on uppercase.
3. **Copy from the results panel**; The newline-separated list pastes cleanly into seeds, fixtures or .env files.

## Example
Requesting five identifiers yields a lowercase batch; each matching the canonical pattern xxxxxxxx-xxxx-4xxx-[89ab]xxx-xxxxxxxxxxxx.

Result for these inputs:

```
Generated UUIDs (v4): 5 random UUIDs, lowercase
```

## About this calculator
### Why v4 dominates

Time-based UUIDs leak creation order and machine identity; v4 offers neither, just 122 bits of raw randomness. Collision probability across trillions of IDs stays negligible, which is why v4 is the default for primary keys, request IDs and idempotency keys.

### Reading the format

- Third group’s first hex digit: version; always 4 here
- First hex of the fourth group: variant 10xx; always 8, 9, a or b
- Everything else: uniformly random hex

## FAQs
### Are these cryptographically secure?

Yes; crypto.randomUUID() uses the platform CSPRNG. In non-secure contexts the documented Math.random fallback degrades gracefully but is weaker.

### Can I use them as database primary keys?

You can, though fully random IDs hurt B-tree locality versus sequential keys. Many teams adopt ULID-style sortable schemes for large tables instead.

### Could two generated UUIDs ever collide?

Theoretically yes, practically no: generating a billion UUIDs per second for a century still leaves collision odds vanishingly small.

### Is a UUID the same as a GUID?

Effectively yes; Microsoft’s GUID term refers to the same 128-bit identifier family; the v4 layout is universal today.

## Related calculators
- [ULID Generator](https://codeasystem.com/calculators/developer/ulid-generator/)
- [Secure Password Generator](https://codeasystem.com/calculators/developer/password-generator/)
- [LLM Token Counter](https://codeasystem.com/calculators/developer/llm-token-counter/)

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Last updated: 2026-08-23 · Version: 1.0.0 · [HTML version](https://codeasystem.com/calculators/developer/uuid-generator/)