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

The annotation readOnlyHint=true already discloses that this is a safe read operation. The description adds what data is included (registered mail, signature, tariffs) but does not disclose any additional behavioral traits such as data freshness, sorting, or whether the list is exhaustive. This is adequate given the low complexity.

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, well-structured sentence that front-loads the core purpose ('De landen waarheen een brief verstuurd kan worden') and then lists the specific attributes. Every word adds value, and there is no redundancy.

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 tool with no parameters, no output schema, and a simple read-only reference list, the description fully covers the necessary information. It explains the type of data (countries), the domain (letters), and the per-country details (registered mail, signature, rates). Nothing essential is missing.

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 zero parameters, the schema provides no input guidance. The description effectively compensates by describing the output domain (countries and per-country attributes), which is more than the empty schema offers. The baseline for zero parameters is 4, and the description fulfills this by giving meaningful context about the returned data.

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 identifies the tool as providing destination countries for letters, with details on registered mail, signatures, and shipping rates. It lacks an explicit verb but its title and content make the purpose unmistakable. It implicitly distinguishes itself from sibling tools like 'bestellen' (ordering) and 'prijs' (pricing) by focusing on the countries themselves.

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 does not state when to use this tool versus the alternatives. It only describes the content of the data, not the context for selecting it. There is no mention of prerequisites, typical use cases, or exclusions.

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