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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, but the description adds meaningful context: it explicitly says the tool does not change page or account state, does not access BetterOff customer data, and does not provide personalized financial advice. This goes beyond the structured annotations and clarifies the tool's non-invasive behavior.

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 concise sentences front-load the core purpose ('Read-only educational calculator'), then state the outputs and inputs, and finish with behavioral guarantees. Every clause earns its place with no filler or repetition.

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 that an output schema exists and annotations cover the safety profile, the description is largely complete for correct invocation. The only minor gap is that feesPaid is not referenced in the description, though its schema entry provides the necessary information. Overall, an agent has enough context to select and call this 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?

Schema description coverage is 100%, so the baseline is 3. The description enumerates several inputs (initial investment, final value, years, dividends) but omits feesPaid, which is present in the schema. Overall, the description adds little semantic value beyond what the schema already documents.

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 opens with 'Read-only educational calculator' and explicitly names the outputs ('total return, annualized return (CAGR), and dollar gain') and inputs ('initial investment, final value, years, and dividends'). This clearly distinguishes it from sibling calculators by stating its specific calculation scope and educational nature.

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 provides clear usage context: it is an educational, read-only calculator that operates on caller-supplied public inputs and does not provide personalized financial advice. It implies when to use it (for simple investment return calculations) but does not explicitly name alternative tools or exclusion conditions, so it stops 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.