EXPLICIT INPUTS. INSPECTABLE ANSWERS.
A calculation layer
for your tools and agents.
HTTP and MCP use the same deterministic engines as the website. Public compute has no account, history, storage, or payment access. Current engine: catalog-2026-10-30.1.
Discover fields before calculating
GET /api/tools/ returns calculator fields, defaults, formulas, assumptions, the engine version and the request JSON Schema. Supply every required input. Defaults are examples, not extracted user facts. Public compute does not save requests to your account or history; do not send secrets or personal records.
Calculate with JSON
POST /api/calculate/ with Content-Type: application/json. Use the canonical trailing slash; clients may deliberately reject redirects. This example returns a primary result of 30. Responses include normalized inputs, the formula, assumptions, protocol and engine version. Errors contain error.code and error.message. Unknown tools return 404, invalid inputs 400, oversized bodies 413, unsupported content types 415 and rate limits 429.
curl https://usecalculator.app/api/calculate/ -H "Content-Type: application/json" --data '{"protocol":"uctool/1","toolId":"percentage","inputs":{"percentage":20,"amount":150}}'Connect an MCP client
Connect to https://usecalculator.app/api/mcp/ using Streamable HTTP. No API key is required for this bounded public compute endpoint. Initialize the connection and use tools/list to discover the live tools: list_calculators and calculate. Capabilities come from the running server, not a static discovery file. The server is stateless and does not offer persistent GET/SSE sessions.
Domain discovery starts at /.well-known/ai-catalog.json, which links to /api/mcp/server-card. The card describes the actual server identity, transport and an exercised protocol version. It follows the current Server Card extension; it does not enumerate tools, invent OAuth support or grant access to accounts. Older scanners may expect a different card shape.
Bounded by design
Requests are limited to 24,000 UTF-8 bytes observed while streaming, a five-second body deadline and at most 32 scalar inputs. Tool-specific fields, choices, dimensions and numeric bounds still apply.
Public tool routes share a limit of 60 requests per trusted transport address per minute. State is process-local. Handle 429 and Retry-After; do not retry in an unbounded loop. A large public launch needs additional edge controls, capacity planning and operating monitoring.
Cross-origin browser computation requests are rejected. Server-side clients can omit Origin. No credentialed CORS access is provided. Discovery documents contain public metadata only. Tools cannot execute arbitrary code, fetch supplied URLs, change user records or silently select a country’s tax rules.
Read public methods as Markdown
Send Accept: text/markdown to the homepage, the developer page, reviewed calculator pages or reviewed guides to request a text representation. HTML remains the browser default. Vary: Accept keeps caches from mixing the representations. A more strongly preferred HTML media type wins.
Only explicitly selected public documents have a text representation. Private pages, authentication, stored sets, shared snapshots, query-bearing URLs and unreviewed tax or language pages do not. The Markdown is generated from published methods; it never includes your current inputs, results or account data.
curl https://usecalculator.app/calculators/contribution-margin/ -H "Accept: text/markdown"Inspect custom definitions and model proposals
UCALC/1 defines bounded custom arithmetic. The builder checks syntax, units, bounds, examples and review signatures. A model proposal remains a draft until its meaning and independent expected answers are checked. A JSON Schema controls structure; it does not establish semantic correctness. No live model provider is activated.
Plan commercial integrations around verified capabilities
Paid API plans, API-key issuance, agent billing and x402 settlement are not activated. Anonymous compute is not a paid API entitlement or a service-level promise. Public account enrollment and live paid checkout have independent release gates. Payment claims from clients never grant access.
Search engines do not require these discovery documents for AI search inclusion. Use them to help compatible clients find an actual interface. Measure completed tasks and retained customers separately from crawler activity or scanner scores.