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

Going beyond the readOnlyHint=true/openWorldHint=false/idempotentHint=true annotations, the description discloses the coverage scope (airports worldwide with IATA codes and scheduled service), the return shape (matched code type and distance in km), and the cost model ($0.05 per successful call via x402/USDC on Base). The pricing detail is genuinely useful behavioral context. It doesn't mention rate limits or caching, but the extra disclosure 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?

Front-loaded with the core verb+resource, then attributes, then the proximity mode, then return/cost. It's a dense two-sentence block with slight redundancy between the title and the first clause, but every element serves a purpose.

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 read-only lookup tool with 100% parameter schema coverage and no output schema, the description covers scope, both invocation modes, return contents, and pricing. The absence of an output schema means the description carries more burden, and it mostly does – only the exact response structure is left implicit, which is minor.

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 schema already documents all five parameters (code, near, limit, country, radius_km) with formats and ranges. The description adds only high-level mode descriptions (code vs. proximity) rather than any per-parameter meaning beyond the schema. Baseline 3 is correct.

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+resource (lookup of an airport by IATA/ICAO code) and names the exact attributes returned (name, city, country, region, coordinates, elevation, IANA tz). It also names a second mode (nearest airports by coordinate), which distinguishes it from all siblings without needing to open a 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?

The two modes are described (code lookup vs. proximity via coordinate+radius), giving clear context for how to call the tool. However, there is no explicit when-not-to-use guidance or named alternative siblings (e.g., geo_distance or country_lookup) that an agent might confuse it with.

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