---
name: usecalculator
description: Discover and run UseCalculator public arithmetic through HTTP or MCP with explicit inputs, units, formulas and assumptions. Use for percentages, pricing, conversions and inspectable calculation tasks.
---

# UseCalculator public computation

Use this skill for bounded arithmetic with explicit inputs. It does not provide account access, storage, tax filing, a live model provider or payments.

1. Read https://usecalculator.app/api/tools/ to find an appropriate calculator, required fields, supported choices, bounds and assumptions. Defaults are examples. Ask the user for missing units, cost definitions or dates rather than treating a default as a user fact.
2. Send only the necessary non-sensitive scalar inputs to https://usecalculator.app/api/calculate/ using POST and Content-Type: application/json. Do not send personal records, credentials or private client data. Follow the user's authorization for external requests.
3. Use this request for a known-answer check:

```json
{"protocol":"uctool/1","toolId":"percentage","inputs":{"percentage":20,"amount":150}}
```

The primary result is 30. Inspect error.code and error.message on a failed HTTP request. Do not invent a result or silently replace the user's inputs after validation fails. Check the directory again if a tool or field is unknown.

4. Report the result together with its units, normalized inputs, formula, assumptions and engine version. Check that the cost basis, period and rounding answer the user's question. Arithmetic validation is not jurisdiction or business review.
5. For MCP, discover the card through https://usecalculator.app/.well-known/ai-catalog.json and connect to https://usecalculator.app/api/mcp/ with Streamable HTTP. Initialize first, then use tools/list. The live tools are list_calculators and calculate. Static discovery is advisory and does not authorize account operations. Persistent GET/SSE sessions are not supported.

## Limits and privacy

The public compute routes share 60 requests per transport address per minute per process. Request bodies are limited to 24,000 UTF-8 bytes, 32 scalar inputs and a five-second body deadline. Respect 429 and Retry-After; keep retries bounded. Server-side clients may omit Origin; do not evade origin checks in a browser. Calculation requests are not saved to user history by this API, which is not a guarantee about infrastructure logging.

Custom formulas remain reviewed proposals. No tool can save or share a set, submit a tax return, execute arbitrary code, browse a supplied URL, charge a customer or settle x402. Do not seek private account cookies or credentials. Use the canonical trailing-slash compute URLs to avoid redirect-sensitive clients.

Read https://usecalculator.app/developers/ for contracts and limits. Public methods also accept Accept: text/markdown on the same canonical document URL.