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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered by structured data. The description adds the scope constraint ('from the UK') and the shape of the returned data, which is modest value beyond the annotations but no further behavioral detail (ordering, completeness of the list, freshness).

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 front-loaded sentence with no filler. The scope qualifier ('from the UK') and returned fields are packed in without 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?

With no output schema and no parameters, the description carries the burden of explaining what comes back, and it does state the returned fields (ISO codes, return support). It is complete for such a simple tool, though it says nothing about whether the list is exhaustive or ordered.

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 tool takes zero parameters, so there is nothing for the description to disambiguate. Baseline 4 applies per the rules; no parameter semantics are missing.

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 gives a specific verb (list) and resource (countries SAMOS ships to from the UK), plus the exact fields returned (ISO codes, return support). That is unambiguous. It does not explicitly differentiate itself from the sibling tools (estimate_duties, estimate_shipping_price, search_help, track_parcel), though the resource is naturally distinct.

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 only implied: an agent infers this is a reference lookup to run before quoting or validating a destination. There is no explicit when-to-use, when-not-to-use, or named alternative, so it sits at the minimum-viable level rather than giving real routing guidance.

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