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

Annotations already cover readOnly/idempotent/openWorld, so the description correctly spends its words elsewhere: the fixed catalog size (261), the unusual inclusion of non-country entities (oceans, EU, World), and the implied alias-style matching of names. It omits any note on truncation behavior when results are capped, but the core behavioral picture is solid.

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, no filler. The scope/payload statement comes first and the usage guidance second, which is exactly the order an agent needs it in.

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?

No output schema exists, and the description compensates by saying entities come back with their Factbook codes and regions. Combined with a fully documented 3-parameter schema and safety annotations, nothing an agent needs to call this correctly is missing.

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% — each of query, region and limit is documented and region carries a full enum. The description adds only the nuance that query matches Factbook naming variants, which is a modest gain over what the schema already says. Baseline 3 applies.

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 concrete verb and resource ('List or search the 261 entities in the CIA World Factbook') and enumerates the exact scope (countries, dependencies, oceans, EU, World) plus the payload (GEC codes and regions). That scope is distinctive enough to separate it from factbook_country or factbook_fields, but no sibling is named to make the distinction explicit.

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 second sentence gives two clear use cases: resolving how the Factbook names a place ('Burma', 'Congo (Brazzaville)', 'DRC') and listing all entities in a region. Concrete examples make the intended trigger obvious, though it never says when to prefer this over factbook_country or entity_profile.

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