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by com.truecalci
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Home loan EMI

home_loan_emi
Read-onlyIdempotent

Calculate reducing-balance monthly Equated Monthly Installment (EMI), total interest payable, and amortization schedule for home, auto, or personal loans.

Behavior: Deterministic, idempotent calculation with zero external side effects. Computes standard monthly EMI formula: E = P * r * (1 + r)^n / ((1 + r)^n - 1), where r = annualRate / 12 / 100. Returns monthly EMI, total payment (principal + interest), total interest percentage, and first-year amortization breakdown.

Usage Guidelines: Use for general global reducing-balance loans and consumer debt. Do not use for US residential mortgages requiring property tax, hazard insurance, and PMI escrow; use mortgage_piti instead.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
principalYesTotal borrowed principal loan amount in currency units. Must be a positive number.
as_of_dateYesCivil date YYYY-MM-DD. Selects the rule pack in force on that date. Required: the engine will not assume a date.
tenureYearsNoTotal loan repayment duration in years (e.g. 15, 20, 30). Must be an integer >= 1.
interestRatePercentYesAnnual interest rate in percent, as a decimal string (e.g. 8.50).

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed2 schema fields changed
    • addedInput schema / properties / as_of_date
      Added value: +{
+  "description": "Civil date YYYY-MM-DD. Selects the rule pack in force on that date. Required: the engine will not assume a date.",
+  "example": "2026-09-26",
+  "pattern": "^\\d{4}-\\d{2}-\\d{2}$",
+  "type": "string"
+}
    • changedInput schema / required
      Previous value: -[
-  "principal",
-  "interestRatePercent"
-]New value: +[
+  "principal",
+  "interestRatePercent",
+  "as_of_date"
+]
  2. Changed7 schema fields changed
    • changedInput schema / properties / interestRatePercent / description
      Previous value: -"Annual interest rate percentage (e.g. 8.5 for 8.5%). Must be positive."New value: +"Annual interest rate in percent, as a decimal string (e.g. 8.50)."
    • addedInput schema / properties / interestRatePercent / example
      Added value: +"8.50"
    • addedInput schema / properties / interestRatePercent / pattern
      Added value: +"^\\d+(\\.\\d+)?$"
    • changedInput schema / properties / interestRatePercent / type
      Previous value: -"number"New value: +"string"
    • addedInput schema / properties / principal / example
      Added value: +"5000000.00"
    • addedInput schema / properties / principal / pattern
      Added value: +"^\\d+\\.\\d{2}$"
    • changedInput schema / properties / principal / type
      Previous value: -"number"New value: +"string"
  3. Changed3 schema fields changed
    • changedInput schema / properties / interestRatePercent / description
      Previous value: -"Annual interest rate %"New value: +"Annual interest rate percentage (e.g. 8.5 for 8.5%). Must be positive."
    • changedInput schema / properties / principal / description
      Previous value: -"Loan amount"New value: +"Total borrowed principal loan amount in currency units. Must be a positive number."
    • changedInput schema / properties / tenureYears / description
      Previous value: -"Loan term in years"New value: +"Total loan repayment duration in years (e.g. 15, 20, 30). Must be an integer >= 1."
  4. First observed

TDQS

A4.3/5.0
Behavior4/5

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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, so the description's statement about deterministic, side-effect-free behavior adds little beyond annotations. However, it does disclose the return fields (monthly EMI, total payment, total interest percentage, first-year amortization breakdown) and the exact formula used, which are not covered by annotations or schema.

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?

The description is organized into three focused paragraphs: purpose, behavior, and usage guidelines. It is front-loaded with the core action and includes the formula for transparency without being verbose. It could be slightly more compact by omitting the formula, but it earns its place.

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?

With no output schema, the description adequately explains the return values (monthly EMI, total payment, total interest percentage, first-year amortization breakdown) and the calculation formula. It also names the alternative for edge cases. It does not mention potential errors or edge conditions, but for a deterministic calculation tool, the provided information is sufficient for correct invocation.

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 each parameter is well-documented in the schema (e.g., principal pattern, interestRatePercent decimal string, as_of_date selection of rule pack, tenureYears default). The description does not add significant parameter-level meaning beyond what the schema provides, so the baseline of 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?

The description opens with the verb 'Calculate' and names the specific resource: reducing-balance monthly EMI, total interest payable, and amortization schedule for home, auto, or personal loans. It clearly distinguishes from the sibling mortgage_piti by specifying that US residential mortgages are out of scope, so an agent can differentiate without inspecting other tools.

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?

Explicitly states when to use ('general global reducing-balance loans and consumer debt') and when not to ('US residential mortgages requiring property tax, hazard insurance, and PMI escrow'), and names the alternative tool (mortgage_piti). This leaves no ambiguity about selection criteria.

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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