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

Goes well beyond the annotations: it discloses that the write is account-persistent and applies across all of My Wine, that it is reversible by calling again with the previous country (which the result reports), and that invalid countries cause a refusal with no state change. These are exactly the side-effect details destructiveHint/idempotentHint cannot convey.

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?

Front-loaded with the action, then persistence scope, then usage constraints, then the argument. Every sentence adds a distinct fact (persistence, undo path, explicit-request constraint, lookup fallback, refusal behavior); there is no filler.

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-param mutating tool with annotations plus an output schema, the description supplies everything else an agent needs: preconditions, persistence semantics, reversal path, and failure behavior. No behavioral gap remains.

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 0%, so the description carries the full burden and does: it states the value must come from list_available_regions, that matching is case-insensitive, and that unrecognized/backend-disallowed values are rejected without mutation. That is complete guidance for the single required param.

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 first sentence gives a precise verb+resource ('Change the user's marketplace region (profile country)'), with a parenthetical clarifying what 'region' means. It is unmistakably distinct from the read-only sibling get_user_region and from the lookup tool list_available_regions.

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?

Explicit when-to-use ('Only call this on the user's EXPLICIT request'), explicit when-not ('never as part of the normal sommelier flow, and never on your own initiative'), and an explicit fallback alternative ('call list_available_regions first'). Nothing about selection is left to inference.

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