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

With no readOnly or destructive hints in annotations, the description carries the full burden. It discloses a key limitation: 'Only sees aeroplanes that are airborne and in range of a receiver — not finding one does not mean the flight was cancelled.' This is valuable behavioral context that goes beyond the schema.

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 description is two sentences, front-loaded with the core action, and includes every necessary detail without waste. Each sentence earns its place: the first states what it does, the second clarifies limitations.

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 simple one-parameter lookup with no output schema, the description provides adequate context: input types, current location, and a key limitation. It does not detail the exact return format, but for a tool like this, the essentials are covered. Sibling tools are not mentioned, but the description stands alone sufficiently.

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?

The schema description already fully covers the single 'flight' parameter with the same examples ('BA117', 'BAW117', 'G-ZBKL'). The description repeats this information without adding new semantics, so it adds no value beyond the schema. Baseline 3 is appropriate given 100% schema coverage.

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 clearly states the tool's purpose: 'Find where an aircraft is right now' with specific input types (flight number, callsign, registration). This distinguishes it from sibling tools like flights_airport and flights_overhead, which are likely about airport information and overhead flights.

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 provides clear context on what identifiers to use (flight number, callsign, registration) but does not explicitly mention when to use this tool versus alternatives like flights_airport or flights_overhead. The usage is implied rather than explicitly contrasted with siblings.

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