Calcgrid: 737 calculators with HTML, Markdown, JSON API, MCP and A2A access

Open deterministic calculation and evidence-data engine for AI agents and people: finance, loans, health, fitness, math, statistics, unit conversion, pinned IANA time-zone rules, science and engineering, plus source-traceable mainland China working days and official UK bank holidays, lunar calendar and solar terms; available as HTML, Markdown, JSON API, MCP and A2A. Every calculator is a documented, deterministic formula available as a web page, a Markdown document, a JSON API endpoint, an MCP tool and an A2A skill. No authentication is required for any calculation.

What this site provides

High-value tasks for AI agents

These balanced starting points show the breadth of Calcgrid while keeping differentiated data capabilities easy to find. Detailed capabilities retain explicit selection boundaries, example prompts and direct typed MCP tools. View the full agent capability guide or read machine-readable JSON.

Compatible browser agents can discover 24 read-only site tools on this page through WebMCP. Other clients can use the same tools through the public MCP server.

Capabilities by category

Machine access

SurfaceURLPurpose
Documentation/docs/index.mdIndex of all capabilities in Markdown; each calculator also has /<category>/<id>.md.
REST API/api/v1GET /api/v1/calculate/{calculator_id}?input=value; list, search and schema endpoints.
Global CLDR weekday baseline/api/v1/data/global-working-dayPinned territory weekend conventions for a worldwide weekday baseline; public holidays are intentionally excluded.
Global public-holiday reference/api/v1/data/global-public-holidaysOpenHolidays nationwide public-holiday reference for supported countries; ODbL provenance, no direct-authority claim and no substitute-day inference.
Working-day calendar selection/api/v1/data/working-day-calendarsRoutes agents to verified jurisdiction packages or the explicitly limited global weekday baseline.
China work-calendar data/api/v1/data/china-work-calendarVersioned full-year working-day records, 调休 exceptions and official State Council provenance.
UK bank-holiday data/api/v1/data/uk-bank-holidaysPinned GOV.UK bank holidays and full-year working-day records for England and Wales, Scotland and Northern Ireland, with source hash and OGL attribution.
IANA time-zone evidence data/api/v1/data/iana-tzdbPinned tzdb release, official artifact SHA-256, license, coverage and supported named-zone identifiers.
OpenAPI 3.1/openapi.jsonEvery endpoint with parameters, types, examples, error codes and rate limits.
MCP server/mcpStreamable HTTP, JSON-RPC 2.0, no auth. tools/list exposes all 253 callable read-only tools.
A2A agent/a2aJSON-RPC message/send and tasks/get; skills listed in the Agent Card.
llms.txt/llms.txtPlain-text overview for language models; /llms-full.txt includes all calculator docs.
ARD/.well-known/ard.jsonAgentic Resource Discovery manifest (MCP server, A2A agent, OpenAPI).
Agent Card/.well-known/agent-card.jsonA2A protocol agent description with skills.
AI plugin manifest/.well-known/ai-plugin.jsonLegacy-compatible OpenAPI discovery descriptor for clients that still look for an AI plugin manifest.
Sitemap/sitemap.xmlAll HTML and Markdown pages.

Example

curl "https://tttkmbb.com/api/v1/calculate/bmi?weight_kg=70&height_cm=175"
{"success":true,"request":{"tool":"calculate_bmi","calculator_id":"bmi","inputs":{"weight_kg":70,"height_cm":175}},
 "result":{"entity_type":"calculation","status":"completed","values":{"bmi":22.86,"category":"Normal weight",...},"units":{"bmi":"kg/m²"},"formula":"BMI = weight_kg / (height_cm / 100)²"},
 "sources":[{"name":"WHO – ...","url":"https://..."}],"freshness":{"type":"static"},"timestamp":"2026-09-23T07:20:14Z","next_actions":[{"tool":"calculate_bmr","reason":"..."}]}

Featured tools (dedicated MCP tools)

Data sources and freshness

All calculators implement published formulas (WHO, NIST, IUPAC, USDA, peer-reviewed papers and standard textbooks); the source list is attached to every calculator page and API response. The global CLDR weekday baseline, mainland China and UK working-day results and named-zone time calculations expose versioned evidence packages. Formula-based results are static (never stale); date calculators that default to "today" are marked freshness.type = "daily". No live market, weather or price data is used.