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

Annotations already establish the read-only, idempotent, non-destructive profile. The description adds useful behavior beyond that: it discloses the full response shape (future value, total contributions, interest earned, effective annual rate, milestones) and the presence of chart_hints rendering directives.

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 compact and front-loaded: calculation disclaimer, return values, use-case guidance, and chart_hints are each given one purposeful sentence. There is no filler or repetition of structured schema 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?

The output list and chart_hints mention compensate for the absence of an output schema. Optional-parameter behaviors like inflation overlay and rate_convention are not described in prose, but the highly detailed schema covers them, so enough context exists 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 description coverage is 100%, so the baseline is 3. The description's mention of 'balance that grows with contributions' minimally reinforces principal and monthly_contribution, but the schema already provides complete meaning for all nine parameters, including units, defaults, and constraints.

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 ('standard compound interest calculator') and enumerates the return metrics. It also distinguishes itself from sibling tools by naming what it is not, so an agent can pick it apart from calculate_opportunity_cost and calculate_loan_payoff without inspecting 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 this tool when a balance grows with contributions and names the conditions under which calculate_opportunity_cost or calculate_loan_payoff should be selected instead. The professional-verification caveat also frames when to treat results as advisory.

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