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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuine value beyond that by disclosing data freshness ('cheapest fares found in the last 48 hours') and that the live price lives on the booking page rather than in the response.

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?

Four short sentences with no padding, but the flight/fare content is arguably off-purpose for a place lookup and dilutes the front-loaded intent. The one genuinely useful constraint (48-hour fare freshness) is buried mid-paragraph.

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 single-parameter lookup with full schema coverage and no output schema, the description is enough to call the tool mechanically, but it leaves the agent unsure whether the tool returns place identifiers, fares, or both, and does not differentiate it from its two siblings.

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?

Only one parameter exists and schema coverage is 100%, with the schema itself giving the Lisbon/LIS example. The description adds no extra meaning about the query string, 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 first sentence ('Look up a city or airport code') states a clear verb and resource, but it is essentially the title restated. The following sentences pivot to cheap flights and cheapest days to fly, which is the domain of the sibling tools cheapest_dates and find_deals, so an agent cannot cleanly tell what the tool itself returns versus what the siblings do.

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?

There is no statement of when to use this tool instead of cheapest_dates or find_deals, and no prerequisites or context for invocation. The note about the live price being on the booking page describes an outcome, not when to call this tool.

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