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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds value by detailing what the calculation includes (taxes, insurance, HOA, PMI) and that it returns lifetime totals and payoff timing. No contradictions with annotations are present.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is only two sentences long, yet it conveys the full scope, an important usage note about state names, and a concrete example. Every sentence earns its place without any fluff or repetition of schema details.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given 10 parameters, complete schema coverage, and no output schema, the description does a good job of summarizing the tool's coverage. It mentions key return elements ('lifetime totals and payoff timing') and one usage pattern. However, it doesn't clarify the mutual exclusivity between state and propertyTaxRatePercent, though the schema does. This is a minor gap in an otherwise complete description.

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

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

Schema description coverage is 100%, meaning every parameter already has a detailed explanation. The tool description does not add meaning beyond the schema; it only reiterates that passing a state uses that state's average property tax rate, which the schema already states. With high schema coverage, a baseline of 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool's purpose: 'Full monthly housing cost for a US mortgage: principal and interest, property tax, homeowners insurance, mortgage insurance and HOA dues, plus lifetime totals and payoff timing.' It uses a specific verb (calculate), a specific resource (mortgage payment), and defines the exact scope. The inclusion of an example ('what would my payment be on a $400,000 house') further anchors the purpose and distinguishes it from sibling calculators.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

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

The description provides a clear use case with the example 'what would my payment be on a $400,000 house', telling the agent when to invoke it. However, it does not explicitly name alternative sibling tools (e.g., calculate_amortization, calculate_pmi) or state when not to use this tool, so it falls short of full exclusionary guidance.

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