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

Annotations already declare readOnlyHint and idempotentHint, so the safety profile is known. The description adds a behavioral fact not in annotations: 'Counts exclude closed airports.' It also clarifies that the dataset is bundled, which is useful context. This goes beyond what annotations provide.

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 sentences, front-loaded with the core purpose. The first sentence states what it does and what it returns; the second covers optional behavior and a caveat. No wasted words, and the structure helps an agent quickly grasp the 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?

With an output schema present, the description doesn't need to explain return format. It covers purpose, usage, optional parameters, and a key exclusion (closed airports). It also links to search_airports, giving the agent enough context to call it correctly. Nothing essential 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%, so the parameters are fully documented in the schema. The description reinforces the meaning of include_regions ('nest each country's regions') and continent restriction, but doesn't add new semantic information beyond the schema. Baseline 3 is appropriate.

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 ('list') and resource (countries in the OurAirports dataset) with output details (ISO codes and airport counts). It also distinguishes itself from siblings by explicitly positioning it as the lookup table for valid country/region filter values used by ourairports_search_airports, making its role clear.

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 gives clear context: it is the lookup table for valid country (and region) filter values for ourairports_search_airports, implying when to use it. It also mentions optional continent filtering and include_regions. It does not explicitly rule out other tools, but the purpose makes the usage obvious.

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