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

Annotations already establish readOnlyHint=true and idempotentHint=true, so the safe, non-destructive nature is covered. The description adds the 'stepping up each year' behavior, but it omits details like compounding frequency or whether contributions are made at the beginning or end of each month, which are relevant for a financial tool.

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 is front-loaded with the core calculation ('Future value') and quickly covers the key nuance ('stepping up each year'). No unnecessary words are present.

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 description is adequate for a straightforward calculator, but it leaves out crucial assumptions such as compounding frequency and contribution timing. While an output schema exists, it is not visible here, and the description alone is somewhat under-specified for a formula with multiple plausible interpretations.

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%, with all four parameters already documented. The description simply echoes 'fixed monthly contribution' and 'stepping up,' providing no additional parameter semantics beyond what the schema already gives.

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 'Future value of a fixed monthly contribution, optionally stepping up each year,' which clearly specifies the tool's purpose. It distinguishes itself from siblings like 'future-value' and 'annuity-fv' by highlighting the step-up feature.

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 when to use this tool—whenever a future value of periodic contributions with possible annual increases is needed—but it does not explicitly contrast with alternatives or state exclusions. This provides only implicit guidance.

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