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

Annotations already declare destructiveHint=true and idempotentHint=true, so the description's added value is the auth constraint ("needs a browser login, not an API key") and the blast radius of changing country_code on all unfiltered queries — context the annotations cannot express. The one gap is that it never states what happens when a parameter is left null.

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?

Three sentences, front-loaded with the auth constraint and the core effect, and the code-lookup pointer is well placed at the end. There is mild redundancy between the first line's "changes the signed-in person's data" and the second sentence's restatement of the same change.

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 annotations, a full output schema, and complete parameter descriptions available, the description covers what it must: auth method, fields affected, side effects on other tools, and where to get valid codes. Only the semantics of null/omitted parameters remain undocumented.

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% and the schema already documents both parameters, so the baseline is 3. The description adds the downstream fallback semantics of country_code and points to list_countries for code values, but does not clarify the meaning of an omitted/null field in this call itself.

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 and resource ("Changes this user's preferred country or language") and scopes it to the signed-in person, which cleanly separates it from siblings like update_my_interests or list_countries. An agent can tell exactly what the 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?

Gives real routing guidance: use list_countries to obtain valid codes, and the country_code preference feeds every other tool's default filtering. It does not explicitly say when to prefer update_my_interests instead, nor when not to call this, so it stops just short of a 5.

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