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

Beyond the readOnly/idempotent annotations, the description discloses accuracy (haversine within ~0.5% of WGS-84), data provenance (OurAirports, error-prone, no endorsement), error semantics (422 unknown_airport, not charged), latency (<0.1s), price, and free-tier rate limits. This is unusually rich behavioral context.

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 purpose and output, then scales to accuracy, sourcing, errors, latency and cost. It is dense but well ordered; the pricing/attribution sentences are borderline but still earn their place for an agent deciding whether to call.

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 no output schema, the description fully carries the return-value burden by enumerating units, bearings and midpoint, and it covers accuracy, errors and cost. Nothing an agent needs to invoke it 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 coverage is 100%, so the baseline is 3, but the description adds a real constraint not in the schema: airport codes are '2-8 characters'. It otherwise restates the code-or-{lat,lon} form already documented.

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 computation (great-circle distance) over specific resources (two airports by code or coordinates), plus the exact output set (km/nautical/statute miles, bearings, midpoint). This clearly distinguishes it from siblings like lookup_airport or geocode.

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?

It gives a clear negative constraint ('Informational only: not for flight planning or navigation') that bounds when to use it, but it never names an alternative sibling to route the agent elsewhere. Clear context, no explicit alternatives.

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