select_region

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

With no annotations, the description carries the full burden; it does contribute real behavioral context by stating the effect is scoped to "this stdio server session" (session state, not account state) and clarifying there are no ordering side effects. It omits whether the choice can be changed later, what happens with an unrecognized country, and whether the session must be authenticated first.

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?

One short, front-loaded sentence with the core action first and the caveat second; nothing is padded. The trailing "does not place orders" clause is borderline filler but earns its place by preempting a wrong interpretation of a checkout-adjacent tool.

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 session-setup tool with no output schema, the description covers the action and side-effect profile but leaves the two things an agent most needs: the accepted country format and the effect of the selection on downstream tools. Adequate but with clear gaps.

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% for the single required parameter, so the schema supplies only the name "country"; the description must compensate and does not. It also introduces a terminology mismatch ("region" vs "country") without stating the accepted format (ISO code, country name, or enum), which is the main risk of a mis-call.

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 ("Select the region") scoped to the session, and the negative clause "does not place orders" separates it from checkout/order siblings like submit_order and checkout_preview. It stops short of naming the closest alternatives or explaining what region selection affects.

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?

There is no explicit when-to-use guidance: nothing says whether this must be called before search_products, delivery_location, or checkout flows, nor whether it is required at all. The only guidance is the exclusion "does not place orders," which rules out one misinterpretation but does not help an agent decide when to invoke it.

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