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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false, and openWorldHint, so the safety profile needs no restating. The description adds one genuinely new behavioral fact — that each call costs 1 credit — but says nothing about rounding, currency assumptions, or error behavior for negative/zero inputs.

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?

Two short sentences front-loaded with the verb, formula, and unit conventions, plus a parenthetical cost note. Nothing is padding and nothing important is buried at the end.

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 a three-parameter pure-calculation tool with full schema coverage and rich annotations, the description covers everything needed to call it correctly. The only mild gap is that no output schema exists and the description does not state the result's format or rounding, though for simple interest that is largely self-evident from the formula.

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%, so all three parameters are already documented with types and examples. The description's note that rate is a percentage and time is in years largely repeats the schema text, adding only the formula that maps the three fields together, which earns a baseline 3 rather than more.

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?

States a specific verb and resource ('Calculates simple interest') and even gives the exact formula, so the computation is unambiguous. The word 'simple' implicitly separates it from the sibling compound_interest, but it never names that alternative explicitly, so differentiation is left to inference.

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 only implied: 'simple interest' suggests it fits flat-rate, single-period calculations, but there is no statement of when to prefer compound_interest, calculate_investment_return, or loan_repayment instead. An agent working from this description alone would have to guess the boundary.

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