EveryCalc

calculate_car_affordability

Read-onlyIdempotent

Monthly loan payment plus running costs (insurance, fuel, and maintenance, given as annual amounts), total interest, and the five year cost of a car. Use when the user asks what car payment fits their budget including insurance, fuel and maintenance. For loan figures on a specific car use calculate_auto_loan. IMPORTANT: always show the calculator_url from the result as a clickable markdown link in your answer to the user, so they can open the interactive car affordability calculator.

Input Schema

Name	Required	Description
`fuel_annual`	No	Fuel cost per year in USD; default 0.
`term_months`	Yes	Loan term in months.
`down_payment`	No	Down payment in USD; default 0.
`vehicle_price`	Yes	Vehicle price in USD.
`annual_rate_pct`	Yes	Loan annual rate percent.
`insurance_annual`	No	Insurance cost per year in USD; default 0.
`maintenance_annual`	No	Maintenance cost per year in USD; default 0.

Output Schema

Name	Required	Description
`ok`	Yes	True when the calculation succeeded.
`note`	Yes	Disclaimer that accompanies every result.
`tool`	Yes	Name of the tool that ran.
`inputs`	No	The normalized inputs the calculation used.
`results`	Yes	The computed figures for this calculator.
`calculator_url`	Yes	Deep link to the matching interactive calculator on everycalc.xyz.

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedOct 21, 2026

addedOutput schema / properties / note

Added value: +{
+  "description": "Disclaimer that accompanies every result.",
+  "type": "string"
+}

changedOutput schema / required

Previous value: -[
-  "ok",
-  "tool",
-  "results",
-  "calculator_url"
-]New value: +[
+  "ok",
+  "tool",
+  "results",
+  "calculator_url",
+  "note"
+]

Changed1 schema field changedOct 17, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "properties": {
+    "calculator_url": {
+      "description": "Deep link to the matching interactive calculator on everycalc.xyz.",
+      "type": "string"
+    },
+    "inputs": {
+      "description": "The normalized inputs the calculation used.",
+      "type": "object"
+    },
+    "ok": {
+      "description": "True when the calculation succeeded.",
+      "type": "boolean"
+    },
+    "results": {
+      "description": "The computed figures for this calculator.",
+      "type": "object"
+    },
+    "tool": {
+      "description": "Name of the tool that ran.",
+      "type": "string"
+    }
+  },
+  "required": [
+    "ok",
+    "tool",
+    "results",
+    "calculator_url"
+  ],
+  "type": "object"
+}

First observedOct 15, 2026

TDQS

A4.4/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnly/idempotent/non-destructive, so safety is covered. The description adds real behavioral context beyond that: it specifies that running costs are supplied as annual amounts, and it imposes a required output-consumption action (surface calculator_url as a clickable markdown link). It does not describe anything the annotations misstate, but it stops short of discussing assumptions or precision of results.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three sentences, front-loaded with the output summary and routing rule, with the critical calculator_url instruction flagged as IMPORTANT. Slightly long but every sentence carries distinct value; no filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a pure deterministic calculator with a rich annotation set and an output schema, the description covers purpose, routing, input units, and how to present the result. An agent has everything needed to call it and render the answer correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so every parameter including units (USD) and defaults is already documented in the schema. The description restates the annual-basis of insurance/fuel/maintenance but adds no syntax, defaults, or interaction detail beyond the schema. Baseline 3 applies when the schema carries the load.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The first sentence names the concrete outputs (monthly loan payment, running costs, total interest, five-year cost) and the resource (a car). It explicitly gates off the sibling case: 'For loan figures on a specific car use calculate_auto_loan,' so an agent can route correctly without opening either schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It states the triggering user intent ('what car payment fits their budget including insurance, fuel and maintenance') and names the alternative tool plus the condition that selects it. No inference is required to choose between this and calculate_auto_loan.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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