Public API

Výnosometr is a free calculator of real estate investment returns in Czechia. The same model is available to scripts and AI agents: an HTTP API, an MCP server, an agent skill and WebMCP tools in the browser. No authentication, no API key. Results are free to use with attribution: cite "Výnosometr (vynosometr.cz)" and link the calculator.

Česky: veřejné API pro výpočet výnosnosti bytu, tržní data po městech, kurz EUR/CZK z ČNB a stav služby. Bez přihlášení, s uvedením zdroje.

Discovery

• API catalog (RFC 9727): /.well-known/api-catalog
• OpenAPI 3.1 description: /api/openapi.json
• Status: /api/health
• MCP server card: /.well-known/mcp/server-card.json
• AI catalog (ARD): /.well-known/ai-catalog.json
• Agent skills index: /.well-known/agent-skills/index.json
• Agent auth: /auth.md (no registration, anonymous access)

POST /api/calc

Investment return of a buy-to-let flat in Czechia: monthly cash flow after Czech taxes, gross and net yield, cash-on-cash, IRR on own funds including the sale and a verdict (green, orange, red). Long-term and short-term (Airbnb) rental. All fields are optional; missing ones are filled with city market defaults. Also available as GET with query parameters. Limit 30 requests per minute per IP.

curl -X POST https://vynosometr.cz/api/calc   -H 'content-type: application/json'   -d '{"city":"brno","price":5500000,"areaM2":55,"rentMonthly":21500}'

Fields: city, rentalType (ltr/str), price, areaM2, rentMonthly, adr, occupancy, downPayment or downPaymentPct, rate, termYears, holdYears, appreciation, renovation, furnishing, lang (cs default, or en: language of the summary and of the calculator link). Money in CZK, rates as decimals (0.052 = 5.2 %). The response contains attribution, the inputs used, results, warnings and openInCalculator, a link that opens the calculator with the same inputs.

GET /api/market

Market assumptions by city: rent and asking price per m², gross yield, typical nightly rate and 10-year price growth. Optional ?city=brno.

MCP server

Streamable HTTP endpoint https://vynosometr.cz/mcp (stateless, JSON responses, no auth) with tools calculate_rental_yield and get_market_data. Add it as a remote MCP server / custom connector in your AI client.

WebMCP

On the calculator pages, browsers with WebMCP (navigator.modelContext) get the tools calculate_rental_yield, get_market_data and fill_calculator, which fills the calculator on the page for the user.

GET /api/kurz

Daily EUR/CZK exchange rate published by the Czech National Bank (ČNB), cached for 6 hours. Returns 503 when ČNB is unavailable.

curl https://vynosometr.cz/api/kurz

{ "eurCzk": 24.315, "date": "29.09.2026", "source": "ČNB" }

GET /api/health

Health of the website and the database. 200 when everything works, 503 when the database is down.

curl https://vynosometr.cz/api/health

{ "ok": true, "web": "ok", "supabase": "ok", "ms": 84 }

Contact

Questions or ideas: kontakt@vynosometr.cz. The calculator itself is at vynosometr.cz/en.