EveryCalc

calculate_mortgage

Read-onlyIdempotent

Monthly mortgage payment breakdown: principal and interest via the amortization formula, plus property tax, homeowner insurance, PMI, and HOA. Use when the user is buying a home and wants the full monthly payment including tax, insurance, PMI and HOA. For a plain loan without housing costs use calculate_loan; for the most they can afford use calculate_affordability. 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 mortgage calculator.

Input Schema

Name	Required	Description
`home_price`	Yes	Purchase price in USD.
`term_years`	No	Loan term in years; default 30.
`hoa_monthly`	No	Monthly HOA dues in USD.
`pmi_rate_pct`	No	Annual PMI rate percent; default 0.5.
`annual_rate_pct`	Yes	Annual interest rate percent, e.g. 6.5.
`down_payment_pct`	No	Down payment percent; default 20.
`down_payment_usd`	No	Down payment in USD (wins over down_payment_pct).
`include_schedule`	No	Include the yearly amortization schedule.
`property_tax_annual`	No	Yearly property tax in USD.
`home_insurance_annual`	No	Yearly homeowner insurance 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

A4.5/5.0

Behavior4/5

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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, so the safety profile is covered. The description adds genuinely non-obvious behavioral context beyond the annotations: the result contains a calculator_url that MUST be surfaced as a clickable markdown link in the answer, which is an output-contract instruction an agent could not infer from schema or annotations.

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

Conciseness5/5

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

Front-loaded with the purpose in the first clause, then usage, then siblings, then a clearly flagged 'IMPORTANT' output requirement. Four sentences, each carrying distinct information with no redundancy or 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 10-parameter, fully schema-documented calculator with an output schema, the description supplies everything the structured fields do not: component scope, routing rules to the two nearest siblings, and the required presentation of the result URL. Nothing an agent needs to call it correctly is missing.

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 coverage is 100%, so every parameter (including defaults for term_years, down_payment_pct, pmi_rate_pct and the down_payment_usd precedence rule) is already documented in the schema. The description only restates the cost components at a high level and adds no format or precedence detail beyond the schema, so the 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 ('Monthly mortgage payment breakdown') and enumerates the exact cost components computed: principal/interest via amortization, property tax, insurance, PMI, and HOA. It also explicitly distinguishes itself from calculate_loan and calculate_affordability by name, so an agent can route without opening any 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?

Gives a concrete use condition ('when the user is buying a home and wants the full monthly payment including tax, insurance, PMI and HOA') and names two alternatives with the conditions that select them ('plain loan without housing costs' → calculate_loan; 'the most they can afford' → calculate_affordability).

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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