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

Annotations already declare read-only, idempotent, non-destructive, closed-world behaviour. The description adds genuinely new context: the estimation method and its key assumption (kg CO₂ derived from fuel flow at ~75% power), so the agent knows the output is an approximation with a stated basis rather than measured data.

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 tight sentences: purpose first, then the scope/row semantics, then the formula and matching rule. No filler, though the formula detail in the final sentence is dense enough to warrant 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?

With an output schema present, return values need no explanation, and annotations cover the safety profile; the description completes the picture by explaining the estimate's basis and row semantics. The one missing piece is sibling differentiation against estimate_fuel_burn.

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 parameters (period enum, flights rows, aircraft, hours) are already documented. The description restates the aircraft-matching semantics (name, ICAO designator, page slug) and the hours-to-CO₂ relationship, adding marginal value over the schema rather than filling a gap.

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+resource ('Estimates the CO₂ from flying hours') and the scope (one aircraft type for a pilot, several for a fleet). It also gives the computation basis (hours × kg CO₂ per flight hour). However, it never names or distinguishes itself from the very close sibling estimate_fuel_burn, which shares the emissions-estimation territory.

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 description explains the input shape (one row per type) but gives no guidance on when to choose this tool over estimate_fuel_burn or the impact tools (get_my_impact, get_api_impact). There are no exclusions, prerequisites, or routing conditions — an agent must infer the choice from parameter availability alone.

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