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

The annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and a closed world, so the safety profile is fully covered by structured data. The description adds that annualization is an optional behavior affecting the output, which is useful context, but nothing about behavior beyond the schema (e.g. rounding of the percentage, handling of edge values) is disclosed.

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?

A single sentence with zero filler that front-loads the outputs and ends with the optional modifier. Every clause carries information an agent needs.

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?

With a complete input schema, an output schema, and full annotation coverage, the description only needs to frame the operation, which it does. It is essentially complete, falling short only of routing guidance among the numerically similar sibling tools.

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 each parameter documented including positivity and range constraints, so the baseline is 3. The description restates the same three concepts (cost, final value, years) without adding format, units, or interpretation guidance 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 names a specific computation (net gain and ROI percentage) plus its two inputs and an optional annualization dimension, so an agent can immediately tell what the tool produces. It does not, however, explicitly differentiate itself from numerically adjacent siblings such as margin_calculator or percentage_calculator.

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?

There is no statement of when to reach for this tool versus the many other finance/percentage calculators (margin_calculator, compound_interest_calculator, percentage_calculator) in the sibling set. Usage is only implied by the formula being described, and no prerequisites or exclusions are given.

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