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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so safety is fully covered. The description adds genuine non-annotation content: that the tool returns two parallel payoff figures and the extra amount the Rule of 78s retains, which is the key behavioral fact for interpreting results. It stops short of stating assumptions (prepayment penalties, rounding) or error 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?

Front-loaded with the domain qualifier and the computed outputs, with the scenario as a short trailing sentence. Dense but every clause carries information; only the parenthetical lender list is arguably expendable.

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 no output schema, the description must convey return semantics, and it does name the three conceptual outputs (Rule of 78s payoff, actuarial payoff, difference). It omits input assumptions and edge-case handling, but for a stateless calculator with four required scalar params this is close to complete.

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 75%, so the schema documents most parameters (amount, payments_made, annual_rate_pct) and the description repeats none of that detail. It also does not clarify the amount-vs-months relationship or what happens when payments_made approaches months, so the baseline of 3 for a mostly self-documenting schema 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 names a specific computation (early payoff) for a specific loan class (precomputed/add-on interest, Rule of 78s) and states both outputs: payoff under Rule of 78s and under the actuarial method plus the difference. It clearly distinguishes itself from generic siblings like loan_payment or payoff_time by domain, though it never names a sibling explicitly.

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?

Usage is conveyed only through a quoted scenario ('why is my payoff different from my balance'), which implies the right context but gives no explicit when-not or routing to alternatives such as payoff_time for simple-interest loans. An agent can infer the intended situation but must guess the boundary cases.

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