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

With no annotations provided, the description carries the full burden. It discloses the key behavioral trait of fallback to documented defaults for missing inputs, and enumerates the outputs produced. However, it does not mention side effects (though likely pure), error behavior, or any constraints such as value ranges. For a calculator, the listed outputs and default behavior provide moderate transparency, but more could be said about edge cases or return format.

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?

The description is a single, front-loaded sentence that starts with the action and then lists the outputs. It is compact with no wasted words. The minor redundancy 'calculator calculator' is a slight stylistic flaw but does not impede comprehension.

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 9 parameters, all documented in the schema, and no output schema, the description compensates by explicitly listing the computed results. It also clarifies the default-fallback behavior. While it does not describe the exact return structure or handle invalid input scenarios, it is reasonably complete for a straightforward calculator 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%, so each of the 9 parameters already has a description and default in the schema. The tool description adds no extra parameter-level meaning beyond what the schema provides, such as units, relationships, or constraints. Thus the baseline of 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?

The description clearly states a specific verb ('Run') and a specific resource ('HMO mortgage calculator'), followed by a precise list of computed outputs (all-in interest rate, monthly payment variants, arrangement fee). It is immediately distinguishable from sibling tools like calculator_describe or enquiry_fields, which serve different purposes.

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 no guidance on when to use this tool versus its siblings. It does not mention any exclusions or alternatives, such as when to use calculator_describe instead. The only usage hint is about missing inputs falling back to defaults, which is a parameter behavior, not a selection criterion.

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