---
license: mit
language:
- en
pretty_name: fixture-entropy
size_categories:
- 1K<n<10K
task_categories:
- text-generation
tags:
- llm-evaluation
- test-data
- diversity
- claude
- synthetic
configs:
- config_name: calls
  data_files:
  - split: train
    path: out/calls.jsonl
---

# fixture-entropy

Author: Dmitriy Semenkevich (dimhold)

This dataset measures how often 2 independent test fixture sets generated by a Claude model share a value, for 7 value types across 7 Anthropic models, against Faker and true random baselines.

Headline, from the repository README: "Ask a Claude model twice for 30 test person names and the 2 lists share at least 1 name in 64 to 98% of pairs, depending on the model. Faker at the same size: 1.29%."

This is a mirror. The canonical home is the Zenodo record and the GitHub repository; the registration, prior work, limitations and full tables live there.

- Paper: https://dimhold.by/papers/fixture-entropy/
- Code and full write up: https://github.com/dimhold/fixture-entropy
- DOI: https://doi.org/10.5281/zenodo.23545744

## Files

| path | what it is |
|---|---|
| `out/calls.jsonl` | every call: prompt, full reply, usage, timing (1366 rows: 1274 main, 66 n100, 26 failed and retried) |
| `out/baseline.json` | Faker, `uuid4` and `random` baseline values used in all tables |
| `out/summary-main.json` | per cell statistics from `report.py` |
| `out/report-main.md` | the same as tables |
| `out/extra-main.txt` | pooled rates, valid UUID recount, frequency lists, n100 pilot (`extra_stats.py`) |
| `out/logs/` | run logs |
| `context-check.json` | what the CLI could load from the environment |

The names, emails, usernames, companies and addresses in the replies are invented by the models; they are the measured data, not real people.

## How it was produced

1274 calls through Claude Code CLI 2.1.302 between 19 and 20 October 2026, each a separate process with no history, from an empty directory with tools, MCP servers and user settings disabled. 7 types, 3 arms (`plain`, `json`, `diverse`), 7 models. The model reported in `modelUsage` matched the one requested in all 1274. Rows with `"ok": false` are failed attempts that were retried. The n100 phase is incomplete and excluded from every conclusion. For publication the local user directory, the clean room path, the account email and a city in 1 reply were replaced with placeholders; nothing else in the journal was changed. Scripts that reproduce every number are in the GitHub repository.

## Licence

MIT, code and data alike.

## Citation

```bibtex
@misc{semenkevich2026fixtureentropy,
  author = {Semenkevich, Dmitriy},
  title  = {fixture-entropy: how often 2 LLM generated test fixtures collide},
  year   = {2026},
  doi    = {10.5281/zenodo.23545744},
  url    = {https://doi.org/10.5281/zenodo.23545744}
}
```