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

Annotations already cover the read-only, closed-world safety profile, so the description's added value is the data-completeness caveat: 'Missing days have no stored price' tells the agent not to interpret gaps as errors or zero fares. It also notes the returned observation dates and source, though it doesn't say whether data can be stale.

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?

Three short sentences: capability, data caveat, exclusions. Front-loaded with what the tool returns, and every sentence earns its place.

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 usefully names the returned fields (fares, observation dates, source) and explains how missing entries appear. The only material gap is cabin selection/default behavior for a 4-parameter tool.

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 0%, so the description must carry parameter meaning; it clarifies 'route and month' and 'per adult' pricing, but never mentions the cabin parameter or its economy default, leaving one of four params unexplained in prose. Schema patterns and the cabin enum do some of the work, so this is a partial compensation rather than a full one.

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 verb and resource ('Reads stored one-way fares per adult for a route and month') with the exact scope and unit of measurement. The word 'stored' plus 'does not start searches' clearly separates it from search_flights_live, and 'does not predict future fares' separates it from get_flight_price_insight.

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 exclusions ('does not start searches or predict future fares') tell an agent when NOT to use it, which effectively routes to the live-search and price-insight siblings. It stops short of naming those siblings or stating the positive precondition (that a prior search must have populated stored fares).

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