EveryCalc

calculate_affordability

Read-onlyIdempotent

Maximum home price affordable from household income using the 28/36 rule. Use when the user asks how much house they can afford on their income. For the payment on a specific home price use calculate_mortgage. 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 home affordability calculator.

Input Schema

Name	Required	Description
`term_years`	No	Loan term in years; default 30.
`down_payment`	No	Cash available for down payment in USD.
`annual_income`	Yes	Gross yearly household income in USD.
`monthly_debts`	No	Existing monthly debt payments in USD.
`back_ratio_pct`	No	Back-end ratio percent; default 36.
`annual_rate_pct`	Yes	Expected mortgage rate percent.
`front_ratio_pct`	No	Front-end ratio percent; default 28.

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 cover the safety profile (readOnly, idempotent, non-destructive), so the description is not burdened there. It adds real value by disclosing the 28/36 methodology and an output-handling requirement (surface calculator_url as a clickable markdown link), which is behavior the schema and annotations do not convey.

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?

Three tight sentences, front-loaded with purpose then usage then the output directive. Every sentence earns its place, including the IMPORTANT callout which is a genuine invocation requirement.

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?

With an output schema present, return values need no explanation, and the description covers purpose, trigger, sibling disambiguation, methodology, and output presentation. 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 description coverage is 100%, so all seven parameters including ratio defaults are documented in the schema. The description adds no syntax, units, or format detail beyond what the schema provides; the 28/36 mention only indirectly maps to front_ratio_pct/back_ratio_pct. Baseline 3 is appropriate.

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 (calculate) and resource (max affordable home price) plus the methodology (28/36 rule), and explicitly distinguishes itself from calculate_mortgage. An agent can tell it apart from the large sibling list 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 an explicit trigger (user asks how much house they can afford on their income) and names the alternative (calculate_mortgage) with the condition that selects it (payment on a specific price). Nothing is left to inference.

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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