TrueCalci

US mortgage PITI

mortgage_piti

Read-onlyIdempotent

Calculate monthly US mortgage payments broken down into PITI (Principal, Interest, Property Taxes, Homeowners Insurance, and Private Mortgage Insurance) along with full 30-year amortization schedule.

Behavior: Deterministic, idempotent calculation with zero external side effects. Computes standard monthly amortization using fixed-rate annuity formula, computes annual property taxes divided by 12, monthly hazard insurance, and conditional PMI (applied automatically if down payment is under 20% until 78% LTV threshold). Returns monthly total, principal/interest component, tax/escrow components, total lifetime interest, and payoff schedule.

Usage Guidelines: Use for US residential home purchase financing and refinancing scenarios. Do not use for international reducing-balance loans without escrow/PMI; use home_loan_emi instead.

Input Schema

TableJSON Schema

Name	Required	Description
`homePrice`	Yes	Total purchase price or appraised property value in currency units (e.g. 450000). Must be positive.
`as_of_date`	Yes	Civil date YYYY-MM-DD. Selects the rule pack in force on that date. Required: the engine will not assume a date.
`interestRate`	Yes	Annual interest rate in percent, as a decimal string (e.g. 6.75).
`loanTermYears`	No	Standard US alias for tenureYears (loan term in years).
`annualPmiPercent`	No	Annual Private Mortgage Insurance premium percentage (e.g. 0.75 for 0.75% of original loan amount).
`downPaymentPercent`	No	Down payment as a percentage of purchase price (e.g. 20 for 20%). Values below 20 automatically trigger PMI calculations.
`annualHomeInsurance`	No	Annual hazard/homeowners insurance premium in currency units (e.g. 1400).
`propertyTaxRatePercent`	No	Annual local property tax rate as a percentage of home value (e.g. 1.2 for 1.2%).

Output Schema

TableJSON Schema

Name	Required	Description	Default
`trace`	No
`status`	No
`currency`	No
`monthlyPI`	No
`as_of_date`	No
`disclaimer`	No
`home_price`	No
`monthlyPmi`	No
`assumptions`	No
`minor_units`	No
`monthly_pmi`	No
`down_payment`	No
`totalPmiPaid`	No
`totalTaxPaid`	No
`isPmiRequired`	No
`rule_ids_used`	No
`totalInterest`	No
`yearlySchedule`	No
`is_pmi_required`	No
`loan_term_years`	No
`totalCostOfLoan`	No
`yearly_schedule`	No
`monthlyTotalPITI`	No
`monthlyPropertyTax`	No
`totalInsurancePaid`	No
`total_lifetime_pmi`	No
`annual_property_tax`	No
`initial_ltv_percent`	No
`total_interest_paid`	No
`annual_interest_rate`	No
`down_payment_percent`	No
`initial_monthly_piti`	No
`monthlyHomeInsurance`	No
`monthly_property_tax`	No
`total_principal_paid`	No
`principal_loan_amount`	No
`annual_hazard_insurance`	No
`total_property_tax_paid`	No
`monthly_hazard_insurance`	No
`is_property_tax_estimated`	No
`property_tax_rate_applied`	No
`total_cost_of_home_and_loan`	No
`total_hazard_insurance_paid`	No
`total_principal_and_interest`	No
`is_hazard_insurance_estimated`	No
`monthly_principal_and_interest`	No
`monthly_piti_after_pmi_cancellation`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedSep 27, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "additionalProperties": true,
+  "properties": {
+    "annual_hazard_insurance": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "annual_interest_rate": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "annual_property_tax": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "as_of_date": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "assumptions": {
+      "type": [
+        "array",
+        "null"
+      ]
+    },
+    "currency": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "disclaimer": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "down_payment": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "down_payment_percent": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "home_price": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "initial_ltv_percent": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "initial_monthly_piti": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "isPmiRequired": {
+      "type": [
+        "boolean",
+        "null"
+      ]
+    },
+    "is_hazard_insurance_estimated": {
+      "type": [
+        "boolean",
+        "null"
+      ]
+    },
+    "is_pmi_required": {
+      "type": [
+        "boolean",
+        "null"
+      ]
+    },
+    "is_property_tax_estimated": {
+      "type": [
+        "boolean",
+        "null"
+      ]
+    },
+    "loan_term_years": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "minor_units": {
+      "type": [
+        "object",
+        "null"
+      ]
+    },
+    "monthlyHomeInsurance": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "monthlyPI": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "monthlyPmi": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "monthlyPropertyTax": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "monthlyTotalPITI": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "monthly_hazard_insurance": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "monthly_piti_after_pmi_cancellation": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "monthly_pmi": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "monthly_principal_and_interest": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "monthly_property_tax": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "principal_loan_amount": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "property_tax_rate_applied": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "rule_ids_used": {
+      "type": [
+        "array",
+        "null"
+      ]
+    },
+    "status": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "totalCostOfLoan": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "totalInsurancePaid": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "totalInterest": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "totalPmiPaid": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "totalTaxPaid": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "total_cost_of_home_and_loan": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "total_hazard_insurance_paid": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "total_interest_paid": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "total_lifetime_pmi": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "total_principal_and_interest": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "total_principal_paid": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "total_property_tax_paid": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "trace": {
+      "type": [
+        "array",
+        "null"
+      ]
+    },
+    "yearlySchedule": {
+      "type": [
+        "array",
+        "null"
+      ]
+    },
+    "yearly_schedule": {
+      "type": [
+        "array",
+        "null"
+      ]
+    }
+  },
+  "type": "object"
+}

Changed3 schema fields changedSep 26, 2026

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"
+}

removedInput schema / properties / tenureYears

Removed value: -{
-  "default": 30,
-  "description": "Loan duration in years (typically 15, 20, or 30).",
-  "type": "integer"
-}

changedInput schema / required

Previous value: -[
-  "homePrice",
-  "interestRate"
-]New value: +[
+  "homePrice",
+  "interestRate",
+  "as_of_date"
+]

Changed7 schema fields changedSep 26, 2026
- addedInput schema / properties / homePrice / example
```
Added value: +"400000.00"
```
- addedInput schema / properties / homePrice / pattern
```
Added value: +"^\\d+\\.\\d{2}$"
```
- changedInput schema / properties / homePrice / type
```
Previous value: -"number"New value: +"string"
```
- changedInput schema / properties / interestRate / description
```
Previous value: -"Annual mortgage interest rate percentage (e.g. 6.8 for 6.8%). Must be positive."New value: +"Annual interest rate in percent, as a decimal string (e.g. 6.75)."
```
- addedInput schema / properties / interestRate / example
```
Added value: +"6.75"
```
- addedInput schema / properties / interestRate / pattern
```
Added value: +"^\\d+(\\.\\d+)?$"
```
- changedInput schema / properties / interestRate / type
```
Previous value: -"number"New value: +"string"
```

Changed8 schema fields changedSep 5, 2026

changedInput schema / properties / annualHomeInsurance / description

Previous value: -"Annual hazard insurance premium"New value: +"Annual hazard/homeowners insurance premium in currency units (e.g. 1400)."

changedInput schema / properties / annualPmiPercent / description

Previous value: -"Annual PMI % if down payment < 20%"New value: +"Annual Private Mortgage Insurance premium percentage (e.g. 0.75 for 0.75% of original loan amount)."

changedInput schema / properties / downPaymentPercent / description

Previous value: -"Down payment percentage (e.g. 20 for 20%)"New value: +"Down payment as a percentage of purchase price (e.g. 20 for 20%). Values below 20 automatically trigger PMI calculations."

changedInput schema / properties / homePrice / description

Previous value: -"Purchase price of the home in currency units (e.g. 450000)"New value: +"Total purchase price or appraised property value in currency units (e.g. 450000). Must be positive."

changedInput schema / properties / interestRate / description

Previous value: -"Annual interest rate in % (e.g. 6.8)"New value: +"Annual mortgage interest rate percentage (e.g. 6.8 for 6.8%). Must be positive."

changedInput schema / properties / loanTermYears / description

Previous value: -"Loan duration in years (standard US alias for tenureYears)"New value: +"Standard US alias for tenureYears (loan term in years)."

changedInput schema / properties / propertyTaxRatePercent / description

Previous value: -"Annual property tax rate %"New value: +"Annual local property tax rate as a percentage of home value (e.g. 1.2 for 1.2%)."

changedInput schema / properties / tenureYears / description

Previous value: -"Loan duration in years (e.g. 15, 20, 30)"New value: +"Loan duration in years (typically 15, 20, or 30)."

First observedSep 5, 2026

TDQS

A4.6/5.0

Behavior4/5

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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the description's 'deterministic, idempotent, zero side effects' line is largely redundant. However, it adds genuinely new behavioral detail: PMI is applied automatically below 20% down until the 78% LTV threshold, and it discloses the calculation basis (fixed-rate annuity, tax/12, monthly insurance). That is useful beyond the annotations, though the repetition of annotation-covered traits keeps it from a 5.

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 clearly labeled sections (description, Behavior, Usage Guidelines) with the purpose front-loaded. Efficient overall, but the Behavior paragraph spends a clause restating annotation-provided traits (deterministic/idempotent/no side effects) that the agent already sees in structured form.

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?

An output schema exists, so return values need not be detailed, yet the description still previews the outputs (monthly total, P&I split, escrow components, lifetime interest, payoff schedule). Combined with the routing guidance and PMI rules, nothing an agent needs to invoke this correctly is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the baseline is 3, but the description adds cross-parameter meaning the schema does not: downPaymentPercent below 20 automatically triggers PMI, and PMI persists until 78% LTV. That explains the interaction between downPaymentPercent and annualPmiPercent rather than merely restating them.

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 (monthly US mortgage PITI payments) and enumerates the components. It explicitly contrasts itself with home_loan_emi, so an agent can distinguish it from siblings 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 explicit when-to-use (US residential purchase and refinancing) and when-not-to-use (international reducing-balance loans without escrow/PMI), naming the alternative tool home_loan_emi. The routing condition is unambiguous.

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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