Zeitro: Mortgage Guidelines

Calculate debt-to-income ratios

calculate_dti

Read-onlyIdempotent

Calculates front-end (housing) and back-end (total) debt-to-income ratios from monthly income and monthly payments, and compares them with the published limits of Fannie Mae, Freddie Mac, FHA, VA and USDA, automated and manual underwriting listed separately. Each limit carries its guideline citation (document, section, version, page, cite_as). With loan_amount, state and family_size it also returns VA's minimum residual income. Pure calculation: an estimate, not an underwriting decision.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "monthly_income": "<monthly_income>",
      "housing_payment": "<housing_payment>"
    },
    "name": "calculate_dti"
  }
}

Input Schema

Name	Required	Description
`state`	No	Two-letter state code of the property, e.g. 'TX'; selects VA's residual income region.
`auto_loans`	No	Monthly auto loan and lease payments. Default 0.
`family_size`	No	Number of people in the household, for VA's residual income table.
`loan_amount`	No	Loan amount in dollars; selects VA's residual income table (below or from $80,000).
`other_debts`	No	Any other monthly debt payments, such as payments on other real estate. Default 0.
`credit_cards`	No	Minimum monthly payments on credit cards and other revolving accounts. Default 0.
`student_loans`	No	Monthly student loan payments as the agency counts them. Default 0.
`monthly_income`	Yes	Gross monthly qualifying income of all borrowers, in dollars.
`housing_payment`	Yes	Proposed total monthly housing payment in dollars: principal and interest, property taxes, insurance, mortgage insurance and HOA dues.
`residual_income`	No	The borrower's monthly residual income by VA's method, compared with VA's minimum.
`installment_loans`	No	Other monthly installment loan payments. Default 0.
`alimony_child_support`	No	Monthly alimony, child support and separate maintenance payments. Default 0.

Output Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

First observedNov 11, 2026

TDQS

A4.4/5.0

Behavior5/5

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

Annotations already cover the read-only/idempotent/non-destructive profile, and the description adds substantial context beyond them: the exact ratio pair computed, that automated and manual underwriting limits are listed separately, that each limit carries a guideline citation, and the disclaimer that this is a calculation, not a decision. The conditional dependency for VA residual income is a genuine behavioral disclosure no annotation could convey.

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 front-loaded sentences with the verb first and no filler; every clause carries information. The parenthetical '(document, section, version, page, cite_as)' is slightly over-specified given an output schema exists, which keeps it just short of a 5.

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?

For a 12-parameter calculation tool with an output schema, the description covers what is computed, which agencies and underwriting tracks are compared, the conditional VA branch, and the interpretational caveat. Nothing needed to call it 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 baseline would be 3, but the description adds cross-parameter meaning the schema cannot: loan_amount, state and family_size jointly activate the VA residual income branch, and payments are framed as feeding either the front-end or back-end ratio. It does not enumerate the debt buckets, which is fine because the schema documents those individually.

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?

Opens with a specific verb and resource: 'Calculates front-end (housing) and back-end (total) debt-to-income ratios from monthly income and monthly payments', then states the agency limits it compares against. An agent can tell exactly what this produces without opening the schema, and it is clearly distinct from sibling tools like calculate_fha_mip.

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?

There is no explicit when-to-use/when-not-to-use framing versus alternatives, only the caveat 'an estimate, not an underwriting decision'. The conditional trigger 'With loan_amount, state and family_size it also returns VA's minimum residual income' gives useful invocation context, but routing guidance is implied rather than stated.

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

All Zeitro: Mortgage Guidelines tools Inspect

Try in Browser

One endpoint for every MCP toolRayrun runs every MCP server behind one URL and holds the credentials. Each call is decided per client, tool, and argument, then recorded.ray.runAd

Glama MCP Gateway

Add one secure layer between your agents and this server.

Resources

Need Help?