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

Annotations already establish read-only, idempotent, non-destructive behavior. The description adds meaningful domain behavior: it specifies what each calculator returns, the rate assumptions, HELOC draw/repayment distinctions, and refinance breakeven output.

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 front-loaded with the estimate purpose and then enumerates modes efficiently. It is dense and delivered as one long sentence, but every clause carries useful mode-specific meaning.

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?

For an 11-parameter calculator with no output schema, the description covers the important assumptions, outputs, and mode-specific behavior. It could more fully specify return fields and edge cases, but the schema handles most parameter detail.

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 coverage is 91%, so the schema already documents most parameters well. The description still adds value by mapping parameters to calculator modes, such as mortgage accepting amount or home_price/down_payment, and refinance using current_rate for savings and breakeven.

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: calculating loan payment estimates, with five named calculator modes. It is clearly distinct from the sibling rate-lookup tools because it computes payments rather than listing rates.

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 for each calculator mode and explains when to pass a rate versus using today's average. It does not explicitly name the sibling tools or say when not to use this tool, so it stops short of full alternative routing.

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