EveryCalc

calculate_student_loan_payoff

Read-onlyIdempotent

Months to pay off a student loan and the total interest, computed month by month exactly as the page does. With an extra monthly payment, also returns the interest and months saved. Returns null fields and never_payoff true when the payment does not cover monthly interest. Payoff dates are not returned because the page derives them from the current date. Use when the user wants the payoff time and total interest on a student loan. For other loans use calculate_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 Student Loan Payoff calculator.

Input Schema

Name	Required	Description
`apr_pct`	Yes	Annual percentage rate percent.
`balance`	Yes	Loan balance in USD.
`extra_payment`	No	Extra monthly payment in USD; default 100, the page default.
`monthly_payment`	Yes	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

A4.7/5.0

Behavior5/5

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

Goes well beyond the readOnly/idempotent annotations by disclosing concrete output behavior: extra_payment also returns interest and months saved, null fields and never_payoff=true when the payment doesn't cover interest, and that payoff dates are deliberately omitted. It even flags the required follow-up action (show calculator_url as a markdown link).

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?

Every sentence is front-loaded and actionable: capability, edge cases, sibling routing, then the mandatory UI instruction. No filler or repetition of the name.

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, the description needn't explain return values, yet it still calls out the non-obvious ones (never_payoff, null fields, calculator_url). For a 4-parameter read-only calculator, an agent has everything needed to invoke and present results 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 the schema already documents every parameter, making a 3 the baseline. The description adds only the note that extra_payment defaults to 100 to match the page default, a marginal gain over structured data.

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 description states a specific verb+resource (months to pay off a student loan and total interest) and its computation method ('computed month by month exactly as the page does'). It explicitly distinguishes itself from siblings by directing other loans to calculate_loan.

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 gives an explicit when-to-use ('Use when the user wants the payoff time and total interest on a student loan') and a when-not/alternative ('For other loans use calculate_loan'). 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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