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 safety profile is covered. The description adds meaningful behavioral context beyond that: the calculation is an estimate only, no approval/underwriting/suitability output, no recommendations, and no retrieval from chats, files, accounts, documents, or the web — a real data-sourcing constraint.

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?

Front-loads the core capability in the first sentence, then layers scope limits and disclaimers. The negative-clause list is somewhat long but each clause rules out a distinct class of misuse, so it mostly earns its place.

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?

With an output schema present, return values need no explanation, and the description covers method scope, data sourcing, and authoritative-source caveats. The remaining gap is guidance on method selection and conditional parameters, which an agent must infer from the schema alone.

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 86%, so the schema already documents principal, annualRate, comparisonRate and remainingTermMonths well. The description names the two penalty methods but does not clarify the method enum values, when comparisonRate is required, or how effectiveDate interacts with the calculation.

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?

States a specific verb and resource — estimating three-months-interest and simplified interest-rate-differential prepayment penalties — which is unambiguous and clearly distinct from siblings like calculate_ltv or calculate_debt_service. An agent can identify the tool's domain 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.

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

Gives clear operating context: works only from explicit, non-identifying numbers in the request, and discharge statements remain authoritative. However, it never names or routes to an alternative tool, nor states when a different sibling (e.g. compare_mortgage_scenarios) should be preferred.

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