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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered. The description adds real behavioral scope: it excludes taxes, insurance and fees from the total, and explains the alternative input paths (loan_amount vs home_price with down_payment_pct). It does not discuss rate limits or error behavior, but that is not essential here.

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?

Three dense sentences with zero filler; the primary output and input-format choice are front-loaded, followed by usage scope and then exclusions. Every sentence 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?

The tool is a stateless calculation with a full output schema, full parameter coverage and clear annotations. The description covers scope, input alternatives and exclusions, so nothing an agent needs to invoke it correctly is missing.

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 100%, so the baseline is 3, but the description adds value beyond the schema by explaining the mutual exclusivity of loan_amount versus home_price plus down_payment_pct and by scoping down_payment_pct to mortgages. That extra routing logic helps an agent choose inputs correctly.

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 — it computes monthly payment, total interest and total paid for a fixed-rate loan — and names the concrete loan categories (mortgage, car, student, personal). This clearly distinguishes it from sibling calculators like smartfin_calculate_investment_return or smartfin_project_savings_growth.

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 explicit triggers ('what a loan costs per month or in total, or how the rate or term changes the cost') and explicit exclusions ('Do not use for variable-rate loans, interest-only loans, or credit cards'). The when-to-use and when-not-to-use guidance is fully articulated.

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