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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description reinforces these by stating 'Every call is read-only and idempotent' and adds new behavioral context: error handling specifics (returns error objects instead of protocol errors) and retry safety. This goes beyond the annotations, justifying a score of 4.

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 concise (5 sentences) and well-structured: purpose first, then usage guidance, example, error behavior, and idempotency note. Every sentence adds value, and there is no redundancy or fluff. The front-loading of purpose makes it immediately actionable.

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 low complexity (3 parameters, simple math) and the presence of an output schema, the description covers all necessary aspects: purpose, usage, error handling, and example. It does not need to repeat the output schema details. The description is complete for an agent to select and invoke the tool correctly.

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 the parameters are well-documented in the schema. The description adds a concrete example with typical input and output, which clarifies expected formats and demonstrates fractions for years. This example provides practical understanding beyond the schema's constraints, earning a 4.

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 clearly states the tool computes an amortized loan payment, specifying the outputs (monthly payment, total paid, total interest). It explicitly distinguishes from interest-free schedules by naming the sibling tool 'installment_plan', which is not in the sibling list but is a relevant alternative. The verb 'compute' and resource 'amortized loan payment' are specific and unambiguous.

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 description explicitly says 'Use for a fixed-rate amortized loan' and 'Not for interest-free schedules' with a named alternative ('installment_plan'). It also clarifies that the tool provides administrative math, not financial advice, setting clear expectations for when to invoke it.

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