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chrischall

compass-mcp

by chrischall
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Local

Calculate max affordable home price

compass_calculate_affordability
Read-onlyIdempotent

Calculate the maximum home price you can afford under the 28/36 DTI rule from income, debts, down payment, and rate, with a full PITI breakdown.

Instructions

Solve for the maximum home price you can afford under the standard 28/36 DTI rule. Inputs: monthly income, recurring monthly debts (car loans, student loans, etc.), down payment, interest rate, and optional property-tax rate / insurance / HOA / loan term. Output: max home price, the binding constraint (front-end vs back-end), and the full PITI breakdown at that price. Same math across the realty MCP cohort (@chrischall/realty-core). No network — pure local math.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
hoa_monthlyNo
back_end_dtiNoBack-end DTI cap as decimal, default 0.36
down_paymentYes
front_end_dtiNoFront-end DTI cap as decimal, default 0.28
interest_rateYesAnnual %, e.g. 6.5
monthly_debtsNoSum of monthly debt payments (car, student loans, etc.)
monthly_incomeYes
loan_term_yearsNoDefault 30, max 50
insurance_annualNo
property_tax_rateNoAnnual % of home price, default 1.1

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed11 schema fields changedv1.1.6
    • addedInput schema / properties / back_end_dti / description
      Added value: +"Back-end DTI cap as decimal, default 0.36"
    • addedInput schema / properties / back_end_dti / exclusiveMinimum
      Added value: +0
    • removedInput schema / properties / back_end_dti / minimum
      Removed value: -0
    • addedInput schema / properties / front_end_dti / description
      Added value: +"Front-end DTI cap as decimal, default 0.28"
    • addedInput schema / properties / front_end_dti / exclusiveMinimum
      Added value: +0
    • removedInput schema / properties / front_end_dti / minimum
      Removed value: -0
    • addedInput schema / properties / interest_rate / description
      Added value: +"Annual %, e.g. 6.5"
    • addedInput schema / properties / loan_term_years / description
      Added value: +"Default 30, max 50"
    • changedInput schema / properties / loan_term_years / maximum
      Previous value: -9007199254740991New value: +50
    • addedInput schema / properties / monthly_debts / description
      Added value: +"Sum of monthly debt payments (car, student loans, etc.)"
    • addedInput schema / properties / property_tax_rate / description
      Added value: +"Annual % of home price, default 1.1"
  2. Changed1 schema field changedv1.0.0
    • changedInput schema / $schema
      Previous value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"
  3. First observedv0.12.1

TDQS

A3.9/5.0
Behavior4/5

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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint=false, so safety is covered. The description adds meaningful context beyond that: the output shape (max price, binding constraint, PITI breakdown) and the determinism note ('No network — pure local math').

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?

Front-loaded with the verb and rule, then inputs, then outputs. Mostly earns its place, though the 'Same math across the realty MCP cohort (@chrischall/realty-core)' line is promotional filler rather than actionable information.

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?

No output schema exists, but the description explicitly enumerates the return values (max price, binding constraint, PITI breakdown), compensating adequately. With 10 params at 60% coverage it is complete enough to call 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 coverage is 60% and the description lists the inputs (income, debts, down payment, rate, optional tax/insurance/HOA/term), but it adds no syntax or format detail beyond what the schema already documents. The mid-level coverage justifies the baseline 3.

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 ('Solve for the maximum home price') and the method (28/36 DTI rule), which cleanly distinguishes it from the sibling compass_calculate_mortgage. An agent can tell what it does 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 Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Usage context is implied by the description ('what you can afford'), but it never explicitly says when to choose this over compass_calculate_mortgage or what preconditions exist. It is inferable but not stated.

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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