Test your prompts.
On every model.
Write a system prompt. Pick test cases. Run on Claude Sonnet 4.6, GPT-5.5, Gemini 2 Pro, and Llama 4 — side by side. See exactly which model is best for your use case. Promote the winner to your team's harness library in one click.
You're guessing about your prompts
Most teams pick a model once and never test alternatives. They tweak prompts blindly. They have no way to know if a 'better' version actually performs better.
The blind workflow
- —Pick whichever LLM is trendy
- —Write prompt by gut feel
- —Hope it works in production
- —Discover failures via user complaints
- —Tweak and pray
The data-driven workflow
- Run prompt across 4 LLMs simultaneously
- See exactly how each behaves
- Score against your eval rubric
- Track regression over model updates
- Promote winner to prod, confidently
Three steps, no setup
Write your prompt
System prompt + user template. Use {{variables}} for test case substitution. We provide starter templates for common patterns (synthesis, classification, reasoning).
Run on 4 LLMs
One click → parallel run on Claude, GPT, Gemini, Llama. Latency, tokens, cost — all captured. ~2 second response.
Score & promote
Define eval criteria. Auto-score every output. Pick the winner. Promote to your team's harness library — versioned, eval-tracked, ready to use.
Real prompt, real outputs, real scoring
What sandbox testing reveals
Stop guessing about your prompts.
Free for 5 users. No credit card.