LLM Output Determinism Tester
Paste 2+ outputs — see how variant your prompt is
📚 Learn more — how it works, FAQ & guide Click to expand
Learn more — how it works, FAQ & guide
Click to expand
LLM Output Determinism Tester
Are your LLM outputs really reproducible? Paste two outputs from the same prompt and measure character/word variance. Most "deterministic" prompts at T=0 still drift 1–10%.
How to use this tool
- 1
Run same prompt twice
Use temperature=0 with seed if your provider supports it.
- 2
Paste both outputs
Output 1 and Output 2 below.
- 3
See variance score
Char + word + length variance + determinism rating.
Frequently Asked Questions
Temperature 0 means deterministic, right?
No. Even at T=0, GPU non-determinism, MoE routing, and batched inference cause variance. OpenAI publishes a `seed` parameter but does not guarantee reproducibility. Anthropic does not expose seed.
When does this matter?
Production agents with assertions, evals, regulated industries (legal/medical), reproducible research, structured output (JSON schema validation breaks if output drifts).
What's a good determinism score?
>95% character match = high determinism (likely safe for prod). 80–95% = drift exists, build retries. <80% = your prompt is non-deterministic, redesign.
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