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

Annotations already indicate readOnlyHint=true, so the safety profile is clear. The description adds valuable behavioral context: specifies that PMI is included only when the down payment is under 20%, and clarifies that the result is a 'headline number' for full PITI. This goes beyond the annotations and gives the agent a solid understanding of the tool's behavior.

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 three sentences and front-loaded with the core value proposition. It is somewhat wordy with phrases like 'lender ads leave out,' but every sentence contributes to understanding the tool's scope and output. It is not excessively long and remains readable.

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 7 parameters and no output schema, the description adequately explains the main functionality and the components included in the computation. It could be more explicit about the exact return format (e.g., monthly payment number vs. breakdown), but the phrase 'headline number' gives a sufficient sense. Overall, it is complete for a calculator tool with well-documented parameters.

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%, with all 7 parameters already documented. The description adds some context (e.g., PMI condition tied to down payment) but does not significantly expand on the schema's parameter documentation. Baseline score of 3 is appropriate when the schema carries the load.

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 computes the true monthly mortgage cost, including principal, interest, taxes, insurance, and PMI. It explicitly distinguishes itself from a simple loan payment by saying 'not just the loan' and emphasizing the full PITI cost, which differentiates it from sibling tools like loan_payment.

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 implies when to use this tool: when you want the full cost of owning rather than just the loan payment. It contrasts with lender ads that omit taxes, insurance, and PMI, giving clear context. However, it does not explicitly name alternative tools or state when not to use this tool.

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