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

Annotations only declare readOnlyHint=false and destructiveHint=false; the description adds the genuinely useful behavioral fact that the value is written to a persistent local JSON file (~/.polopan/region.json) and survives across turns and sessions. It does not say what happens on an unrecognized region or whether validation failures are possible, which keeps it below a 5.

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?

Two sentences, both front-loaded: the first covers accepted inputs, the second covers the persistence side effect. No filler and no repetition of the title.

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?

There is no output schema, and the description covers the action, the input flexibility, and the side effect, which is nearly everything an agent needs to call a 2-parameter setter. It omits error/validation behavior for invalid regions and whether the call requires prior authentication.

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 the baseline is 3, but the description adds real semantic value by enumerating the accepted input variants (natural name, city, ISO-2, currency) and giving concrete examples that clarify the loosely typed 'country' string. It does not explain the interaction between the 'country' and 'mode' parameters.

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) and resource (active shopping country/region) and implicitly distinguishes itself from region.get_current and region.list_supported by describing the write action and what it accepts. An agent can tell exactly what this tool mutates without opening the schema.

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 gives a rich and explicit set of accepted input forms (country name, city, ISO-2 code, currency) and explains the persistence rationale. It stops short of naming sibling alternatives (e.g., region.list_supported to discover valid values, region.get_current to read the current value), so routing is implied rather than stated.

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