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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the agent knows this is a safe, non-mutating local computation (openWorldHint=false). The description adds the useful detail that it returns the charge, the benefit kept, and the starting income, but says nothing about rounding, threshold basis, or whether the taxYear default affects results. With annotations covering the safety profile, 3 is appropriate.

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?

One tight sentence with the purpose front-loaded and the outputs listed as a compact clause. No filler, no restatement of the title.

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 read-only three-parameter computation whose annotations already carry the safety profile and whose schema fully documents inputs, the description covers purpose and outputs adequately. The absence of an output schema slightly raises the bar, but listing the three return values largely closes that gap; a note on the income threshold would make it complete.

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% – each of adjustedNetIncome, annualChildBenefit, and the taxYear enum is fully documented in the schema. The description adds no syntax, format, or defaulting detail beyond what the schema already provides, so the baseline 3 applies.

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 ('Calculate') and a precisely named domain resource (the High Income Child Benefit Charge), and enumerates the three outputs the tool produces. It is instantly distinguishable from the many other 'calculate_*_tax' siblings because it names the exact UK charge rather than a generic tax category.

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 the use case (someone with adjusted net income above the threshold who receives Child Benefit) but never states when to reach for this tool versus siblings like calculate_tax_on_multiple_incomes or get_tax_position, nor does it mention the threshold condition or exclusions. Adequate minimum-viable framing, nothing more.

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