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

Beyond the annotations (read-only, idempotent, closed-world), the description discloses deterministic behavior: rounding half up to two decimals, returning the sum plus the ratio percentage, and explicitly omitting comparison bands or classification. It does not mention error behavior for invalid income, but the added behavioral detail exceeds the annotation baseline.

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?

One dense sentence front-loads the arithmetic scope and then the output/rounding behavior; every clause carries information. Slightly packed, but nothing is redundant or padded.

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 two-parameter calculator with an output schema, the description covers inputs, the operation, and the rounding/output shape. Missing only edge-case handling (e.g., non-numeric or over-limit inputs), which the schema largely constrains already.

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 both parameters are already documented, including numeric limits and the empty-array-means-zero rule. The description adds the count cap ('up to 100 payments') and 'positive' income, both of which mirror schema constraints rather than adding new semantics.

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?

Names a specific verb+resource (sum monthly debt payments and divide by gross monthly income) and states the scope 'arithmetic on entered numbers only', which separates it from fetch/classification-style siblings. The clause 'no comparison bands or classification' further distinguishes it from other ratio-style tools an agent might consider.

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 phrase 'entered numbers only' implies when this tool applies (user-supplied figures, not looked-up data) and rules out classification workflows, but no alternative sibling is named and there is no explicit when-not guidance. Usage is implied rather than stated.

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