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

Annotations already declare readOnlyHint=false and destructiveHint=false, so the mutation/safety profile is covered. The description usefully adds that the change is persisted to ~/.polopan/region.json and scoped per-country, but it does not say whether an existing default for that country is overwritten or what happens if the address belongs to a different country.

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 the verb first and zero wasted words. The persistence path is appended without diluting the core action.

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 one-parameter mutation with no output schema and safety annotations already present, the description covers what changes and where it is stored. It stops short of describing replacement semantics for an existing default or error conditions, but nothing critical for invocation 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?

Schema description coverage is 100% for the single address_id parameter, so the baseline is 3. The description only reinforces that the address must be 'existing' and implies its country drives the scope; it adds no format or validation detail beyond the schema.

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 (set as default), the resource (an existing saved address), and the scope (default shipping address for its country). This clearly separates it from address.save (create), address.delete, and region.set_current (region-wide default).

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 word 'existing' implies a precondition that the address must already be saved, which implicitly routes creation to address.save, but no sibling is named and there is no explicit when-to-use/when-not guidance. Usage is inferable rather than stated.

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