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

Annotations already declare readOnlyHint=true and idempotentHint=true, so the agent knows it is a safe, repeatable read. The description adds valuable behavioral detail that contributions are paid at period end, which affects timing of calculations. This 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?

Two sentences, zero filler. The first sentence states the core function and the second positions it relative to siblings. Every word earns its place.

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 five parameters and the presence of an output schema, the description covers the core behavior, contribution timing, and generalization to sibling tools. No necessary context is missing for a mathematical calculator tool.

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 covers all parameters with descriptions, so baseline is 3. The description adds useful semantic context by explaining that periodsPerYear=1 corresponds to future-value and periodsPerYear=12 corresponds to contributions, clarifying defaults and typical usage 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 clearly states the tool computes compound growth at any frequency with optional periodic contributions, and explicitly distinguishes it from sibling tools by noting it generalizes future-value and contributions. The purpose is unmistakable.

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 names sibling tools future-value and contributions, explaining how periodsPerYear=1 maps to future-value and periodsPerYear=12 maps to contributions. This provides concrete guidance on when to use this general tool versus those alternatives.

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