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

Annotations already declare readOnlyHint, idempotentHint, and closed-world, so safety is covered. The description adds real value beyond them by disclosing that the tool performs three distinct computations, including the reverse gross-up ('what to charge to receive the full amount after fees'), which an agent would not otherwise know to expect. It still omits rounding/currency conventions.

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 no filler, front-loading the core computation and packing the three outputs into a tight parenthetical plus clause. Nothing could be cut without losing an output mode.

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?

No output schema exists, so the description must signal the return shape, and it does by naming the three results. With only one required parameter and full schema coverage, little else is needed. Minor gap: no statement of rounding or currency assumptions for a money tool.

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%, including defaults and examples for fixed_fee and percent_fee, so the schema carries the burden. The description only restates that the fee is percentage plus fixed, without adding syntax or interaction detail. Baseline 3 applies when the schema is this complete.

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 ('work out') and resource (card payment fee) and enumerates the three results computed: fee, net proceeds, and gross-up amount. It clearly distinguishes itself from checkers and generic calculators by naming the fee structure (percentage plus fixed fee). It does not explicitly differentiate from percentage_calculator, which is the nearest overlapping sibling.

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?

Usage is implied: use when you need card processing fee math. There is no explicit statement of when to prefer this over percentage_calculator or vat_calculator, and no exclusions or prerequisites. An agent can infer the fit from the resource name, but must make the choice alone.

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