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

Annotations already cover readOnly/openWorld/non-destructive, and the description adds a meaningful trait they don't: the result set can be empty on first call while background pricing kicks off, requiring a retry. That asynchronous, possibly-incomplete behavior is exactly the kind of thing annotations cannot express.

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 first sentence is a long run-on enumeration of return categories that partly duplicates the output schema, and the key operational fact (empty cache triggers pricing, retry later) is buried at the end. It is readable but not tightly front-loaded.

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 covering return values and annotations covering the safety profile, the description only needed to add the async empty-result behavior, which it does. Parameter and return documentation are adequately covered elsewhere, so the definition is essentially complete.

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 from/to/month are already documented in the schema. The description's fare-type listing describes return content rather than adding syntax or constraints to the parameters, so 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?

The description states a specific resource (all fare data held for one airport pair) and enumerates the kinds of fares returned, so the agent knows exactly what it retrieves. It does not, however, differentiate itself from the sibling cheapest_routes, leaving the agent to infer the boundary.

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 line 'If we hold nothing yet, it starts pricing the route and says so; ask again a minute later' gives concrete retry guidance for the empty-cache case, which is genuinely useful. But it never says when to reach for this tool versus cheapest_routes, so alternative selection is left implicit.

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