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

The description discloses that the tool returns both the rule-of-72 estimate and the exact figure, adding behavioral detail beyond the annotations. It also provides the mathematical formulas, which is useful context for the agent.

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 a single concise sentence that front-loads the core purpose ('Years to double') and includes all necessary details without wasted words.

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 simple one-parameter calculation with an output schema present, the description sufficiently explains what the tool does, including both the estimate and exact formula. No further context is needed for the agent to select and use 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?

The input schema already fully documents ratePct as 'Growth rate in percent.' The description mentions 'rate' in formulas but doesn't add new semantic information about the parameter. Since schema coverage is 100%, a baseline 3 is appropriate.

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 explicitly states the tool calculates 'Years to double' via the rule-of-72 estimate and the exact formula, making the purpose clear and distinguishing it from sibling financial calculators. It names the specific resource (rule-of-72) and the output.

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 opening phrase 'Years to double' provides a clear context for when to use this tool. However, it does not explicitly mention alternatives or when not to use it, so it falls short of a 5.

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