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

Annotations already declare readOnlyHint, idempotentHint, non-destructive, and closed-world, so the safety profile is covered. The description adds genuinely useful context beyond that — results are restricted to nonstop routes, each line carries dates and a source-checked timestamp, and an embed address is included — which matters because no output schema exists. It still omits pagination, result-size limits, and the no-argument case.

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, front-loaded with the resource and scope, then the mode enumeration before the output description. The parenthetical '(that airport listed first)' is well-placed, though the compressed 'one airline's, every airline's from one airport ... or both' phrasing takes a second read.

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 low-complexity, read-only listing tool with no output schema, the description covers the query modes and the shape of returned lines reasonably well. The notable gap is that both parameters are optional and the description never says what happens with neither supplied — all routes, an error, or a default — which an agent could easily hit.

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 both parameters are already documented as to format and examples, making 3 the baseline. The description does add real meaning the schema cannot: that supplying airport puts that airport first in the output and that airline and airport can be combined, which is behavioral semantics beyond the field docs.

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 concrete verb and resource ('Nonstop routes on Lounge Frog's route maps') and enumerates the three query modes, so an agent can tell this apart from get_airline, get_airport, and list_airlines. It stops short of naming those siblings explicitly, so differentiation is inferred from the resource rather than stated.

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?

Usage is implied by the enumeration of modes (one airline, one airport, or both), which tells an agent the valid combinations but not when to prefer this tool over get_airport, get_airline, or list_airlines. There are no exclusions or prerequisites, so the agent must infer the routing decision.

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