# UUID Batch Generator

> Draws 16 cryptographic random bytes for each identifier, replaces the RFC 9562 version and variant bits, and renders up to 10,000 UUIDv4 values as a copyable table with a downloadable CSV artifact.

Use it: https://tessalor.com/en/generators/uuid-generator

This tool runs entirely in the browser. Nothing entered into it is uploaded.

## How it is done

1. Validate a whole-number batch size from 1 to 10,000. Allocate 16 bytes per UUID and fill them from Web Crypto in calls no larger than its 65,536-byte quota.
2. In octet 6, preserve its low four random bits and replace the high four with 0100, the version 4 field. In octet 8, preserve its low six random bits and replace the high two with 10, the RFC variant.
3. Render the 16 octets as 32 hexadecimal digits. Canonical form inserts hyphens in the 8-4-4-4-12 grouping; compact removes them; URN adds the urn:uuid prefix. Letter case changes no bit.
4. Compare canonical values inside the current batch and report any duplicate actually observed. Render every value as a static result row that can be copied or downloaded as CSV.

## Assumptions

- Each UUID starts from browser cryptographic random bytes, not Math.random and not a user-visible seed. Six structural bits leave 122 random bits per value.
- Random UUIDs make collisions extraordinarily unlikely; they do not make a mathematical uniqueness guarantee. The batch duplicate count is an observation, not proof against a value generated elsewhere.
- UUIDs are identifiers, not authentication secrets. RFC 9562 says not to assume they are hard to guess or use mere possession as an access capability.
- The generated values are not placed in the URL, saved to catalogue preferences or sent to a server. Recomputing intentionally produces a new batch.

## Inputs

| Name | Label | Type | Default | Range |
| --- | --- | --- | --- | --- |
| `quantity` | How many UUIDs | integer | 20 | 1 to 10000 |
| `format` | Text format | select | canonical |  |
| `letterCase` | Hexadecimal letters | select | lowercase |  |

## Outputs

- `generated` — UUIDs generated (integer), primary
- `randomBits` — Random bits in each UUID (integer)
- `duplicates` — Duplicates in this batch (integer)
- `format` — Representation (text)

## Questions

### Are UUIDs generated on this page sent to a server?

No. Web Crypto fills the random bytes in this browser, the version and variant bits are set locally, and the table exists only in the rendered result. The generated browser test fails if normal tool use makes an off-origin request.

### How many random bits does a version 4 UUID contain?

122. A UUID has 128 bits in total; four identify version 4 and two identify the RFC variant. RFC 9562 assigns the other 122 bits to random data.

### Can two UUID v4 values ever be the same?

Yes in principle, because generation is random, but the space contains 2^122 possibilities. The chance stays tiny at ordinary batch sizes, and this page also reports a duplicate if one occurs inside the current list.

### Is compact or uppercase UUID text a different identifier?

No. Hyphens, hexadecimal letter case and the urn:uuid prefix are representations around the same 128 bits. Use the shape the receiving database or API expects.

### Should a UUID v4 be used as an API key or password?

No. RFC 9562 explicitly warns against assuming UUIDs are hard to guess or using possession as an access capability. Generate a dedicated secret with the length and handling rules appropriate to authentication.

## Sources

- [RFC 9562: Universally Unique IDentifiers (UUIDs)](https://www.rfc-editor.org/rfc/rfc9562.html) — RFC Editor / Internet Engineering Task Force, applies to Standards Track, May 2024. Retrieved 2026-08-01.
- [Web Cryptography Level 2](https://www.w3.org/TR/webcrypto/) — World Wide Web Consortium, applies to Candidate Recommendation Draft, April 2025. Retrieved 2026-08-01.

## Variants

- [How do I generate 100 UUID v4 values at once?](https://tessalor.com/en/generators/uuid-generator/generate-100-uuid-v4-values)
- [How do I generate a GUID list without uploading anything?](https://tessalor.com/en/generators/uuid-generator/generate-guid-list-without-uploading)

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Estimate, not advice. See https://tessalor.com/en/disclaimer.
Machine-readable catalogue: https://tessalor.com/api/tools.json