{ "openapi": "3.1.1", "info": { "title": "Bill Detective API", "version": "1.0.0", "summary": "Spot spikes, price changes and calculation errors across your utility bills.", "description": "Every endpoint performs the same calculation as the human page and returns inputs, result, units, assumptions, sources, warnings and computedAt. MCP endpoint: /mcp." }, "servers": [ { "url": "https://billdetective.usefulweb.site" } ], "paths": { "/api/v1/calculate": { "post": { "operationId": "calculate", "summary": "Spot spikes, price changes and calculation errors across your utility bills.", "description": "Enter several billing periods of an electricity, gas, water or data bill. Bill Detective normalises consumption per day, flags unusual periods (outliers), unit-price and standing-charge changes, and totals that do not add up, each with a plain-English explanation.\n\nMethodology:\n- Days = end date − start date + 1 (both dates count). Consumption per day = consumption ÷ days. Periods are sorted by start date.\n- Computed total = consumption × unit price + fixed charge + other charges. A mismatch is flagged when |total billed − computed| > tolerance % × computed (minimum 0.01).\n- Consumption change: per-day consumption vs. the previous period; flagged when the absolute change exceeds the threshold (default 25%).\n- Above average: per-day consumption more than the threshold above the average of all periods.\n- Outliers (IQR rule, only with ≥ 4 periods): per-day value above Q3 + 1.5 × IQR or below Q1 − 1.5 × IQR, quartiles by linear interpolation.\n- Outliers (median rule): per-day value more than X% (default 30%) above the median per-day value.\n- Unit price change: any change vs. the previous period. Fixed charge change: both the fixed charge per period and the fixed charge per day differ from the previous period by more than 1% (so a flat monthly fee over months of different length, or a fixed daily rate, is not flagged).\n- Gaps and overlaps between consecutive periods are reported as information.", "tags": [ "money" ], "x-mcp-tool": "bill_detective", "requestBody": { "required": true, "content": { "application/json": { "schema": { "$ref": "#/components/schemas/BillDetectiveInput" }, "examples": { "example1": { "summary": "Monthly electricity with a winter spike and a price rise", "value": { "unit": "kWh", "currency": "EUR", "periods": [ { "label": "Jan", "startDate": "2026-01-01", "endDate": "2026-01-31", "consumption": 310, "unitPrice": 0.32, "fixedCharge": 12, "totalBilled": 111.2 }, { "label": "Feb", "startDate": "2026-02-01", "endDate": "2026-02-28", "consumption": 280, "unitPrice": 0.32, "fixedCharge": 12, "totalBilled": 101.6 }, { "label": "Mar", "startDate": "2026-03-01", "endDate": "2026-03-31", "consumption": 300, "unitPrice": 0.32, "fixedCharge": 12, "totalBilled": 108 }, { "label": "Apr", "startDate": "2026-04-01", "endDate": "2026-04-30", "consumption": 290, "unitPrice": 0.35, "fixedCharge": 12, "totalBilled": 113.5 }, { "label": "May", "startDate": "2026-05-01", "endDate": "2026-05-31", "consumption": 520, "unitPrice": 0.35, "fixedCharge": 14, "totalBilled": 198 }, { "label": "Jun", "startDate": "2026-06-01", "endDate": "2026-06-30", "consumption": 295, "unitPrice": 0.35, "fixedCharge": 14, "totalBilled": 117.25 } ] } }, "example2": { "summary": "Quarterly water bills", "value": { "unit": "m3", "currency": "GBP", "periods": [ { "label": "Q1", "startDate": "2025-01-01", "endDate": "2025-03-31", "consumption": 24, "unitPrice": 2.1, "fixedCharge": 18, "totalBilled": 68.4 }, { "label": "Q2", "startDate": "2025-04-01", "endDate": "2025-06-30", "consumption": 26, "unitPrice": 2.1, "fixedCharge": 18, "totalBilled": 72.6 }, { "label": "Q3", "startDate": "2025-07-01", "endDate": "2025-09-30", "consumption": 31, "unitPrice": 2.25, "fixedCharge": 18, "totalBilled": 87.75 } ] } } } } } }, "responses": { "200": { "description": "Calculation result envelope.", "content": { "application/json": { "schema": { "$ref": "#/components/schemas/BillDetectiveResult" } } } }, "400": { "description": "Malformed JSON body.", "content": { "application/problem+json": { "schema": { "$ref": "#/components/schemas/Problem" } } } }, "422": { "description": "Invalid input (see errors[]).", "content": { "application/problem+json": { "schema": { "$ref": "#/components/schemas/Problem" } } } }, "429": { "description": "Rate limit exceeded (see Retry-After).", "content": { "application/problem+json": { "schema": { "$ref": "#/components/schemas/Problem" } } } } } } }, "/api/v1/tool": { "get": { "operationId": "getToolDefinition", "summary": "Inputs, output schema and examples for this tool", "responses": { "200": { "description": "Tool definition.", "content": { "application/json": { "schema": { "type": "object" } } } } } } } }, "components": { "schemas": { "Problem": { "type": "object", "description": "RFC 9457 problem details. 422 responses include per-field `errors`.", "required": [ "type", "title", "status", "detail" ], "properties": { "type": { "type": "string" }, "title": { "type": "string" }, "status": { "type": "integer" }, "detail": { "type": "string" }, "code": { "type": "string" }, "errors": { "type": "array", "items": { "type": "object", "required": [ "field", "message" ], "properties": { "field": { "type": "string" }, "message": { "type": "string" } } } } } }, "BillDetectiveInput": { "type": "object", "additionalProperties": false, "properties": { "unit": { "title": "Consumption unit", "type": "string", "enum": [ "kWh", "m3", "liters", "GB" ], "default": "kWh" }, "currency": { "title": "Currency", "type": "string", "maxLength": 8, "default": "EUR" }, "changeThresholdPercent": { "title": "Flag per-day change vs. previous period above", "type": "number", "minimum": 1, "maximum": 1000, "default": 25, "x-unit": "%" }, "outlierPercent": { "title": "Flag periods above median by more than", "type": "number", "minimum": 1, "maximum": 1000, "default": 30, "x-unit": "%" }, "tolerancePercent": { "title": "Arithmetic tolerance", "description": "Billed total may differ from consumption × unit price + charges by this much (rounding, taxes included in prices) before it is flagged.", "type": "number", "minimum": 0, "maximum": 50, "default": 1, "x-unit": "%" }, "periods": { "title": "Billing periods", "description": "Start and end dates are both counted as billing days. Fixed charge = total standing/base charge for the period. Leave Total billed empty to skip the arithmetic check for a row.", "type": "array", "minItems": 2, "maxItems": 36, "items": { "type": "object", "additionalProperties": false, "properties": { "label": { "title": "Period", "type": "string" }, "startDate": { "title": "Start date", "type": "string", "format": "date" }, "endDate": { "title": "End date", "type": "string", "format": "date" }, "consumption": { "title": "Consumption", "type": "number", "minimum": 0 }, "unitPrice": { "title": "Unit price", "type": "number", "minimum": 0 }, "fixedCharge": { "title": "Fixed / standing charge", "type": "number", "minimum": 0, "default": 0 }, "otherCharges": { "title": "Other charges", "type": "number", "default": 0 }, "totalBilled": { "title": "Total billed", "type": "number", "minimum": 0 } }, "required": [ "label", "startDate", "endDate", "consumption", "unitPrice" ] } } }, "required": [ "periods" ] }, "BillDetectiveResult": { "type": "object", "additionalProperties": false, "required": [ "schemaVersion", "tool", "computedAt", "inputs", "summary", "result", "units", "assumptions", "sources", "warnings", "presentation", "links" ], "properties": { "schemaVersion": { "type": "string", "const": "1.0" }, "tool": { "type": "object", "additionalProperties": false, "required": [ "id", "name", "version" ], "properties": { "id": { "type": "string" }, "name": { "type": "string" }, "version": { "type": "string" } } }, "computedAt": { "type": "string", "format": "date-time" }, "inputs": { "type": "object", "description": "Normalised inputs actually used, including applied defaults." }, "summary": { "type": "string" }, "result": { "type": "object", "additionalProperties": false, "required": [ "unit", "currency", "averagePerDay", "medianPerDay", "periods", "anomalies", "anomalyCount" ], "properties": { "unit": { "type": "string" }, "currency": { "type": "string" }, "averagePerDay": { "type": "number" }, "medianPerDay": { "type": "number" }, "iqr": { "type": [ "object", "null" ], "additionalProperties": false, "required": [ "q1", "q3", "lowerFence", "upperFence" ], "properties": { "q1": { "type": "number" }, "q3": { "type": "number" }, "lowerFence": { "type": "number" }, "upperFence": { "type": "number" } } }, "anomalyCount": { "type": "integer" }, "periods": { "type": "array", "items": { "type": "object", "additionalProperties": false, "required": [ "label", "startDate", "endDate", "days", "consumption", "perDay", "changeVsPreviousPercent", "vsAveragePercent", "unitPrice", "fixedCharge", "fixedChargePerDay", "computedTotal", "totalBilled", "difference", "costPerDay" ], "properties": { "label": { "type": "string" }, "startDate": { "type": "string", "format": "date" }, "endDate": { "type": "string", "format": "date" }, "days": { "type": "integer" }, "consumption": { "type": "number" }, "perDay": { "type": "number" }, "changeVsPreviousPercent": { "type": [ "number", "null" ] }, "vsAveragePercent": { "type": "number" }, "unitPrice": { "type": "number" }, "fixedCharge": { "type": "number" }, "fixedChargePerDay": { "type": "number" }, "computedTotal": { "type": "number" }, "totalBilled": { "type": [ "number", "null" ] }, "difference": { "type": [ "number", "null" ], "description": "Total billed − computed total." }, "costPerDay": { "type": "number", "description": "Billed total (or computed total if not given) ÷ days." } } } }, "anomalies": { "type": "array", "items": { "type": "object", "additionalProperties": false, "required": [ "period", "type", "severity", "explanation" ], "properties": { "period": { "type": "string" }, "type": { "type": "string", "enum": [ "consumption-change", "above-average", "outlier-iqr", "outlier-median", "unit-price-change", "fixed-charge-change", "arithmetic-mismatch", "period-overlap", "period-gap" ] }, "severity": { "type": "string", "enum": [ "info", "warning", "alert" ] }, "explanation": { "type": "string" } } } } } }, "units": { "type": "object", "additionalProperties": { "type": "string" } }, "assumptions": { "type": "array", "items": { "type": "string" } }, "sources": { "type": "array", "items": { "type": "object", "additionalProperties": false, "required": [ "title" ], "properties": { "title": { "type": "string" }, "url": { "type": "string" }, "publisher": { "type": "string" }, "retrievedAt": { "type": "string" }, "note": { "type": "string" } } } }, "warnings": { "type": "array", "items": { "type": "string" } }, "presentation": { "type": "array", "items": { "type": "object" }, "description": "Display blocks used by the human page (same data)." }, "links": { "type": "object", "additionalProperties": false, "required": [ "human", "api", "openapi", "methodology" ], "properties": { "human": { "type": "string", "format": "uri" }, "api": { "type": "string", "format": "uri" }, "openapi": { "type": "string", "format": "uri" }, "methodology": { "type": "string", "format": "uri" } } } } } } } }