EveryCalc

calculate_lease_vs_buy

Read-onlyIdempotent

Lease outlay over the lease term versus buy outlay net of equity in the car at the same point, with the winning option and the net cost difference. Use when the user compares leasing a car against buying it. For loan-only figures 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 lease vs buy calculator.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "msrp": "<msrp>",
      "lease_months": "<lease_months>",
      "lease_monthly_payment": "<lease_monthly_payment>",
      "residual_pct": "<residual_pct>",
      "buy_rate_pct": "<buy_rate_pct>",
      "buy_term_months": "<buy_term_months>"
    },
    "name": "calculate_lease_vs_buy"
  }
}

Input Schema

Name	Required	Description
`msrp`	Yes	Vehicle MSRP in USD.
`buy_rate_pct`	Yes	Buy loan annual rate percent.
`lease_months`	Yes	Lease term in months.
`money_factor`	No	Lease money factor, for example 0.0025; default 0.
`residual_pct`	Yes	Residual value as a percent of MSRP at lease end.
`buy_term_months`	Yes	Buy loan term in months.
`buy_down_payment`	No	Buy down payment in USD; default 0.
`lease_down_payment`	No	Lease down payment in USD; default 0.
`lease_monthly_payment`	Yes	Lease monthly payment in USD.

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

A4.3/5.0

Behavior4/5

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

Annotations already declare a safe read (readOnlyHint, idempotentHint, non-destructive), so the description only needs to add context. It does: it discloses what the result contains (winning option, net cost difference, calculator_url) and an operational requirement to render that URL as a clickable markdown link in the reply. No permissions, limits, or failure modes are discussed, but those are minor for a pure calculator.

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 short sentences, front-loaded with what is computed, then when to use it, then the required follow-up action. Every sentence carries information, though the capitalized instruction is longer than strictly necessary and could be tightened without losing meaning.

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

Completeness4/5

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

An output schema exists, so return values need not be explained; the description still adds the key result fields and the URL-linking obligation. Combined with named alternatives and a clear trigger, an agent has enough to call this correctly, with only edge-case behavior (invalid inputs, which term drives the comparison) left implicit.

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% and every one of the nine parameters carries its own description (MSRP, residual percent, money factor, down payments, terms), so the schema does the heavy lifting. The description restates the comparison framing (lease term versus buy at the same point) but adds no units, defaults, or syntax beyond what the schema already provides. Baseline 3 applies.

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?

States a specific verb-and-resource pair with scope: lease outlay over the lease term versus buy outlay net of equity, plus the winning option and net cost difference. It also names the sibling it is not (calculate_auto_loan for loan-only figures), so an agent can separate it from the loan calculators without opening the 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?

The trigger is explicit ('Use when the user compares leasing a car against buying it') and the nearest alternative is named with the condition that selects it ('For loan-only figures use calculate_auto_loan'). The when-not case is covered by routing loan-only questions away.

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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