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

Annotations already indicate a safe, read-only, idempotent, non-open-world operation, but the description adds substantial behavioral context: VAT/reverse-charge handling, currency conversion with an ECB rate plus margin, international registered-mail behavior, and printing/posting locations.

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 front-loaded and information-dense rather than padded. It is long, but for an 8-parameter pricing tool with VAT, currency, and shipping nuances, most sentences earn their place.

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?

With no output schema, the description carries the burden of explaining return values and does so: total, line items, envelope, size class, zone, delivery time, and VAT/currency treatment. It is complete enough for an agent to invoke and interpret the result 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?

The schema covers 75% of parameters, so many fields are already documented. The description still adds useful meaning for currency conversion, registered mail, destination, print options, envelope sizing, and VAT context, though it does not explicitly explain every parameter such as postal_code.

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 states a precise verb and resource: get a price quote for sending a physical letter by post, including registered mail. It clearly distinguishes this from composing/sending letters and from unrelated email, fax, parcel, or postcard costs.

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?

It gives an explicit trigger: use when the user asks what it costs to send a physical letter by post. It also states exclusions, clarifies registered/certified terminology, and notes that sign-in is not required.

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