Show HN: Tarmac – Know what Claude Code will cost before you run it (github.com)

2 points by sarthakaggarwal 4mo ago ↗ HN

I built this because I kept getting surprised by Claude Code bills. A complex refactoring task that I expected to cost $2 would end up costing $15, and there was no way to know beforehand.

Tarmac analyzes your prompt and gives you a cost range before Claude Code starts working. It uses conformal prediction trained on 3,000 real SWE-bench tasks — hitting 81% in-range accuracy on an 80% target.

npm install -g tarmac-cost — fully open source, runs locally, no tracking, no accounts.

Would love feedback on estimate accuracy for your use cases - that's what I'm most focused on improving

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sarthakaggarwal 4mo ago ↗

Happy to answer any questions about the approach. The key insight is that conformal prediction gives you calibrated confidence intervals — if we target 80% coverage, we actually get 81% of actual costs landing within the predicted range. No ML runtime needed, just feature extraction + dot product. Runs in ~5ms per estimate.

Biggest limitation right now: it only sees the prompt text, not your codebase or conversation history. Short/vague prompts get wide ranges.