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

The annotations already declare this is read-only, idempotent, non-destructive, and open-world, so the description need not repeat the safety profile. It adds useful scope limits: the rate is an assumption, returned costs are excluded from an all-in budget, schedule output is opt-in, and no account or loan application is involved. The phrase 'Returns excluded costs' is slightly ambiguous but still signals a bounded calculation.

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 core purpose is front-loaded in the first sentence, and the remaining sentences add useful scope caveats without rambling. It is compact for a tool with multiple behavioral limits, though the caveat sentences are dense and slightly overlap with annotation-provided information.

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 the output schema, rich annotations, and mostly described input schema, the description supplies the remaining non-obvious context: rate assumptions, excluded costs, opt-in schedule generation, and no account or application requirements. An agent has enough information to invoke it correctly without needing a broader housing-budget interpretation.

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 80%, so most parameters are already documented well in the input schema. The description reinforces the meaning of annualRatePct as an explicit assumption and includeSchedule as opt-in, and it refers generally to extra-payment scenarios. However, it adds little parameter-level detail beyond the schema, so baseline 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 states a specific verb and resource: calculate monthly loan payments, total interest, and extra-payment scenarios from explicit principal, annualRatePct, and years. It also distinguishes the tool's assumption-based calculation from a bank quote, which helps separate it from rate-fetching or affordability siblings.

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?

It gives clear usage context by saying the rate is a stated assumption rather than a bank offer and that the result is not an all-in housing budget. It also says to request includeSchedule only for a detailed repayment table. It does not explicitly name sibling alternatives such as get_mortgage_rates or get_affordability, so it falls short of full when-to-use guidance.

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