API & MCP

Everything a person can do on Sizewise, a program or AI agent can do with the same inputs and get the identical result.

HTTP API

• GET https://sizewise.usefulweb.app/api/v1/tools – catalog
• GET https://sizewise.usefulweb.app/api/v1/tools/{id} – inputs, output schema, examples
• POST https://sizewise.usefulweb.app/api/v1/tools/{id}/calculate – run a tool
• GET https://sizewise.usefulweb.app/api/v1/workflows · POST https://sizewise.usefulweb.app/api/v1/workflows/{id}/run
• OpenAPI 3.1: /openapi.json · /openapi.yaml
• Errors: application/problem+json; 422 includes per-field errors.

Tools on Sizewise

• Sizewise Scale Comparison – Line up buildings, animals, planets or atoms side by side, drawn to true scale. sizewise_scale_compare
• Sizewise How Many Fit – How many Earths fit in the Sun, golf balls in a room or pallets in a trailer? sizewise_fit_count
• Sizewise Big Number Explainer – What does a googol, 2^64 or 8 billion really mean? Names, digits and counting time. sizewise_big_number
• Sizewise Money Stack – How tall is a million dollars? Banknotes as a stack, by weight and on pallets. sizewise_money_stack
• Sizewise Life in Weeks – Your life as a grid of weeks: one row per year, with milestones and exact counts. sizewise_life_weeks
• Sizewise Rate Counter – Turn “so much per year” into per second, project it, and embed a live counter. sizewise_rate_counter
• UnitProof Unit Calculator – Unit maths you can audit: dimension check, exact factors and a full derivation tree. unitproof

Every result contains

inputs (normalised, defaults applied), summary, result (validated against the published schema), units, assumptions, sources, warnings, computedAt and links.

MCP (Model Context Protocol)

• Streamable HTTP endpoint: https://sizewise.usefulweb.app/mcp – protocol revisions 2026-07-28 (stateless) and 2025-11-25 / 2025-06-18 / 2025-03-26 (initialize handshake).
• Tools: sizewise_scale_compare, sizewise_fit_count, sizewise_big_number, sizewise_money_stack, sizewise_life_weeks, sizewise_rate_counter, unitproof
• Local stdio connector: node src/mcp-stdio.ts

{
  "mcpServers": {
    "usefulweb": { "type": "http", "url": "https://sizewise.usefulweb.app/mcp" }
  }
}