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

Annotations already declare readOnlyHint=true, openWorldHint=true, and idempotentHint=true, covering safety and idempotency. The description adds value by disclosing the default filtering behavior (excludes aggregates) and the optional inclusion of aggregate entities, which is not fully captured by annotations. It also specifies the metadata fields returned, giving the agent a clearer picture of the output. No contradiction exists.

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?

The description is two concise sentences: the first establishes the tool's purpose and content, and the second explains the default and the flag to change it. There is no redundancy, and the most important information (what it lists and the default) is front-loaded. Every sentence earns its place.

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 a full input schema and an output schema present, the description does not need to detail return formats. It adequately covers the core behavior (listing, filtering, aggregate control) and aligns with the annotations. An agent can correctly invoke the tool for a listing task without missing essential information, given the schema and annotations cover the rest.

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 all five parameters are documented in the schema with meaning. The description restates the filters and include_aggregates, but adds no new semantic nuance beyond what the schema already provides (e.g., it does not explain interaction effects or pagination behavior). Given the schema's thoroughness, the description adds minimal extra value, aligning with the baseline of 3.

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 description states a specific verb ('Lists') and a clear resource ('countries and regional aggregates'), and enumerates the metadata included (ISO codes, region, income level, capital, coordinates). It distinguishes itself from siblings like worldbank_get_country by focusing on listing, while also clarifying the default exclusion of aggregates. This is unambiguous and directly informative.

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 provides clear context on when to use the tool (to list countries) and explains the default behavior (individual countries only) and how to opt into aggregates (include_aggregates=true). However, it does not explicitly mention alternative tools or state when not to use it, such as when a specific country is needed. Thus it meets the 'clear context, no exclusions' bar but stops short of explicit alternative routing.

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