HomeCalc — Canadian Mortgage & Tax Calculators

Canadian Mortgage Payment Calculator

mortgage_payment

Read-only

Periodic payment on a Canadian mortgage. Pass EITHER homePrice + downPayment (CMHC insurance is added under 20% down) OR loanAmount alone when the user gave the mortgage amount (e.g. "payment on a $500,000 mortgage"). Never invent a purchase price to reach a loan amount: it shifts the answer and adds a CMHC premium the user may not owe.

Input Schema

Name	Required	Description	Default
`province`	No	Province name, used only for CMHC PST on the premium
`rateType`	No	Fixed or variable rate	fixed
`homePrice`	No	Purchase price in CAD, with downPayment. Omit if the user gave the mortgage amount.
`termYears`	No	Mortgage term in years
`loanAmount`	No	Mortgage amount in CAD, instead of homePrice. No CMHC premium is added.
`downPayment`	No	Down payment in CAD, or percent if downPaymentType='percent'. Required with homePrice.
`downPaymentType`	No	downPayment as dollars or percent of homePrice	amount
`paymentFrequency`	No	How often payments are made	monthly
`amortizationYears`	No	Amortization in years (max 25 insured, 30 uninsured/first-time new builds)
`annualInterestRatePct`	Yes	Annual interest rate as a percent, e.g. 5.25

Schema Changelog

Changes observed during successful MCP inspections.

Changed9 schema fields changedNov 2, 2026

removedInput schema / $schema

Removed value: -"https://json-schema.org/draft/2020-12/schema"

addedInput schema / examples

Added value: +[
+  {
+    "annualInterestRatePct": 5.25,
+    "downPayment": 65000,
+    "homePrice": 650000
+  }
+]

changedInput schema / properties / downPayment / description

Previous value: -"Down payment amount in CAD (or percent if downPaymentType='percent'). Required when homePrice is used."New value: +"Down payment in CAD, or percent if downPaymentType='percent'. Required with homePrice."

addedInput schema / properties / downPaymentType / description

Added value: +"downPayment as dollars or percent of homePrice"

changedInput schema / properties / homePrice / description

Previous value: -"Purchase price in CAD, e.g. 650000. Use with downPayment. Omit if the user gave you the mortgage amount instead."New value: +"Purchase price in CAD, with downPayment. Omit if the user gave the mortgage amount."

changedInput schema / properties / loanAmount / description

Previous value: -"The mortgage amount itself in CAD, when the user stated the loan rather than the purchase price. Mutually exclusive with homePrice. No CMHC premium is applied on this path — the amount is taken as the principal."New value: +"Mortgage amount in CAD, instead of homePrice. No CMHC premium is added."

addedInput schema / properties / paymentFrequency / description
```
Added value: +"How often payments are made"
```
addedInput schema / properties / rateType / description
```
Added value: +"Fixed or variable rate"
```
addedInput schema / properties / termYears / description
```
Added value: +"Mortgage term in years"
```

First observedOct 15, 2026

TDQS

A4.6/5.0

Behavior4/5

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

Annotations already declare readOnlyHint/destructiveHint=false, so safety is covered; the description adds genuine domain behavior beyond that — CMHC insurance is auto-added under 20% down and not added when loanAmount is supplied. It stops short of describing the returned figure (per-period amount, total interest, insurance breakdown), which matters since there is no output schema.

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 sentences, front-loaded with the purpose, then the input-mode rule, then the failure mode to avoid. Every sentence carries distinct information with no restatement of schema fields.

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?

For a 10-parameter, single-required-parameter calculator with no output schema, the description covers the highest-risk decision (which input mode) and a silent-error trap. The remaining gap is that it never tells the agent what the response contains, forcing the agent to infer the return shape.

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 baseline is 3, but the description adds real semantic value the schema cannot: that homePrice and loanAmount are alternative entry points rather than complementary parameters, and why substituting one for the other is wrong. It does not, however, clarify the interaction of province, termYears, or paymentFrequency beyond what the schema already says.

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 opening sentence names the exact output (periodic payment) and the precise domain (Canadian mortgage), which separates it from siblings like mortgage_affordability, minimum_down_payment, and mortgage_penalty. An agent can identify the tool's job without opening the 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?

It explicitly routes between two mutually exclusive input modes (homePrice + downPayment vs loanAmount alone) and gives the trigger condition ('when the user gave the mortgage amount', with an example utterance). It also states a when-not with the reason ('never invent a purchase price to reach a loan amount: it shifts the answer and adds a CMHC premium').

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

All HomeCalc — Canadian Mortgage & Tax Calculators tools Inspect

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