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

Annotations already declare readOnlyHint and idempotentHint, so the description only needed to add behavioral context. It does so by explaining that monthly contributions are part of the comparison and by setting an expectation that the low-fee portfolio 'ends materially higher,' which helps the agent understand the class of result.

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 two sentences with the action verb and subject front-loaded, followed by a compact JSON example that demonstrates realistic values. No filler or redundant restatement of the schema appears.

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 seven-parameter calculator with a full input schema, output schema, and safety annotations, the description is complete enough: it states the computation, includes a worked example, and implies the comparative outcome. The output schema handles return-value details, so nothing essential is missing for correct invocation.

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 100%, so the parameters are individually documented in the schema. The description adds a concrete example mapping portfolio, monthly, highFee, lowFee, and years to expected behavior, which communicates parameter relationships beyond the schema.

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 opens with 'Compare how much a high management fee costs versus a low fee over time,' a specific verb and resource that tells the agent exactly what the tool computes. It does not, however, explicitly distinguish itself from sibling tools such as compare_investments, so it stops short of full differentiation.

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 implies a use case for fee-impact comparisons but gives no explicit when-to-use guidance and no conditions for choosing an alternative tool. With siblings like compare_investments and compound_interest available, the absence of routing guidance leaves the agent to infer appropriateness.

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