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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false, and openWorldHint=false. The description adds important behavioral context beyond annotations: invalid input never raises a protocol error, returns an {error: ...} object with remediation, and retry is safe after correcting input.

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 core purpose and output values, then moves through usage, error behavior, and retry safety. It is slightly longer than strictly necessary for a simple math tool, but the structure is clear and most sentences contribute useful information.

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?

Given the simple computation, complete parameter schema, annotations, and presence of an output schema, the description is complete enough to use the tool correctly. It covers purpose, example input/output, appropriate use, exclusions, and error handling.

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, ranges, and constraints. The description reinforces the parameters through a typical input example, but it does not add substantial semantic meaning beyond what the schema already provides.

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: computing an amortized loan payment, including monthly payment, total paid, and total interest. It also distinguishes the use case from interest-free installment schedules, so the agent can identify the correct tool without opening sibling schemas.

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 explicitly says to use the tool for a fixed-rate amortized loan and explicitly says not to use it for interest-free schedules, naming installment_plan as the alternative for that case. This gives clear when-to-use and when-not-to-use guidance.

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