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

Annotations already establish readOnlyHint=true, destructiveHint=false and openWorldHint=false, so safety is covered. The description adds real context beyond that: it computes from the user's own calculator values and returns comparison-table links, provider pages, and quote links where available.

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?

Front-loads the core behaviour (rank by cost) and the geography, then appends illustrative examples. No padding, though the example list is slightly long relative to the rest.

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 tool with no output schema and a nested inputs object, the description covers what it computes, what it returns, and the supported markets. It omits how rankings are presented (ordering, result count) and the defaulting/ignored-input behavior, which is left to the schema.

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?

With 100% schema coverage the baseline is 3, but the description earns a step up by explaining what the generic 'inputs' object represents (card volume, average sale, employees, users) and by naming the three supported markets, giving meaning beyond the slug-only schema docs.

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 and resource ('Ranks providers in a category by estimated monthly cost'), plus the scoping constraint (user's own numbers, US/UK/AU). An agent can distinguish it from the only sibling, list_categories, without opening a schema.

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?

Concrete examples ('EFTPOS and card machine fees', 'cheapest payroll software', 'POS system costs') make the intended context clear, and the schema routes category slugs to list_categories. It stops short of explicitly stating when NOT to use it or naming list_categories as a prerequisite step in the description itself.

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