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

Annotations already cover the safety profile (readOnlyHint=true, destructiveHint=false, openWorldHint=false), and this is a pure computation, so little behavioral disclosure is needed. The description adds value by naming the outputs (future value, total contributed, interest earned), which matters because there is no output schema.

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 tight sentences with zero filler, front-loading what the tool computes and then what it returns. Nothing is redundant or buried.

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 six-parameter calculator with one required field, no output schema, and full schema coverage, the description covers the core behavior and compensates for the missing output schema by listing return values. It stops short of explaining compounding assumptions or defaults, but the schema carries those.

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 all six parameters (principal, rate, years, contrib, compound, timing) are already documented in the schema, establishing a baseline of 3. The description adds only marginal meaning, clarifying that monthly contributions are optional and that the result is a future value.

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?

States a specific verb (grow a balance) and resource (compound interest) plus the distinguishing feature of optional monthly contributions. It is clearly a compounding calculation tool, but it does not explicitly separate itself from near-siblings like simple_interest, savings_growth, or cagr, leaving the agent to infer the boundary.

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 use this tool versus the many financial siblings (simple_interest, savings_growth, rule_of_72, dividend_reinvestment). The mention of 'optional monthly contributions' hints at the scenario but gives no exclusions, prerequisites, or alternative routing.

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