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

Annotations already declare read-only, idempotent, open-world, non-destructive behavior, so the bar is low. The description adds genuinely new context beyond that: fares/walking legs/transfers/boarding instructions are returned, and bus times derive from published timetables rather than live tracking, which sets a freshness expectation the annotations cannot convey.

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?

Two compact sentences with no filler; the capability and mode/region scope are front-loaded and the data-source caveat is placed last as a qualifier. Every clause carries information.

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 and rich annotations, the description need not describe return values, and it correctly focuses on modes, regions, and the timetable-vs-live caveat. The only meaningful gap is the absence of any routing guidance relative to the sibling planning tools.

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% with nested pickup/destination lat-lng objects fully documented in the schema, so the baseline of 3 applies. The description adds no parameter-level meaning (e.g., that coordinates are the only inputs and no departure time is accepted), so nothing pushes it above baseline.

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 ('Plan public transport') and enumerates the output content (fares, walking legs, transfers, boarding instructions) plus supported modes/regions. It doesn't explicitly contrast itself with the overlapping sibling plan_trotro_route, so it falls short of full sibling differentiation.

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?

Geographic scope is implied as a usage condition ('trotro in Ghana, or buses ... in England, Scotland and Wales'), and the 'not live tracking' caveat hints at when results are trustworthy. However, it never names an alternative tool or states when to pick a sibling such as plan_trotro_route or plan_trip instead.

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