The same model, for agents.
A stateless interface to the comparison used in the browser. Explicit assumptions in, reproducible results out.
England · 2026/27 · Model 2026-09-06.1 · Reviewed 6 September 2026
Choose REST or MCP
POST JSON to /api/v1/working-days/calculate, or call compare_working_days through the site’s existing /mcp server. Reading this guide does not install an MCP tool. Your agent client must explicitly register and enable that server.
Explicit inputs, no inferred household
The strict input contract requires every field. Use OpenAPI for types and limits and the complete example JSON as an openly labelled starting template. Obtain the user’s figures; do not present sample values as their situation. All nine scenario keys are required in the quote and estimate records, even when only three are currently compared. Unused partner inputs are retained but ignored for a one-adult household. Unknown bills, benefits, living costs and pension denominators use explicit nulls; zero means a confirmed zero.
curl https://decisionsmadeeasier.com/api/v1/working-days/calculate -H 'Content-Type: application/json' --data-binary @working-days-input.json
Read results without inventing a winner
Responses disclose modelVersion, schemaVersion, taxYear, rulesAsOf, effectiveInputs and an empty substitutedDefaults list. Monetary values are GBP; cashMonthly and extraCashMonthly are monthly, while other monetary totals and time are annual. dcPension is money contributed this year. dbPension is extra annual pension income earned for retirement. Never add those pension quantities together. Null cashMonthly means this scenario is incomplete or unsupported: explain its errors and do not rank it using partial components. The comparisons report adjacent main-adult patterns with the partner held fixed. There is no automatic recommendation.
Scope and missing information
Schema version 1 accepts England and tax year 2026-27 only, with regular equal monthly PAYE and a full year in each pattern. Bills and eligibility stages remain constant. Universal Credit and other awards must be provided from an external calculation for each scenario. Only explicitly confirmed exceptions may waive childcare minimum earnings tests. These are annual decision estimates, not a benefits entitlement service, payslip reproduction or personalised financial advice.
Transport and privacy
The browser calculates locally. Deliberate API and MCP requests send inputs to Vercel; handlers are stateless, do not intentionally log or persist bodies or results, and return no-store responses. REST permits cross-origin callers and publishes POST/OPTIONS only. The request limit is 32,768 UTF-8 bytes; malformed JSON returns 400, oversized bodies 413, wrong content type 415, invalid contracts 422 and unsupported methods 405. Valid requests can return 200 with incomplete scenarios and null cash. MCP retains the existing origin, size, method and no-store controls. Its published edge rate limit covers /mcp; no additional edge-rate-limit claim is made for this REST route.
Machine-readable evidence
MCP resources working-days-methodology and working-days-sources publish the same methodology and source register as these pages. The rent-versus-buy model and its existing schema/version remain unchanged. Working-days inputs, output schema and model version are separate.