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

Annotations already provide readOnlyHint and openWorldHint. The description adds meaningful behavioral context by explaining the ETA source priority (official real-time data, falling back to the own estimation engine) and describing the computed outputs. There is no contradiction with the annotations; the real-time nature even helps justify why idempotentHint is false.

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 dense sentences with no filler. The first sentence defines the task and the calculation logic; the second states the outputs. Key information is front-loaded and every part 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 takes on the burden of explaining return values, and it does so by naming the four decision outcomes, the margin, and the next reachable step. However, it leaves 'siguiente paso alcanzable' somewhat ambiguous and does not describe failure behavior for missing ETA or invalid stops, though UNKNOWN partially covers that.

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 coverage is 100%, so the baseline applies: the schema already documents each parameter with ranges, defaults, and purpose. The description provides a useful global context by linking lat/lng and walk_speed_ms to the walking-time calculation, but it does not add much detail beyond what the schema already conveys.

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 names a specific action ('Decide si el usuario llega a tiempo a un autobús'), a concrete resource (a bus stop in Alicante), and the core method (comparing vehicle ETA with walking time). It also lists the decision outputs (CATCH, TIGHT, MISS, UNKNOWN), which clearly distinguishes it from siblings such as next_departures or find_transit_stop.

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 triggering scenario is explicit: use this tool when the user needs to know whether they can reach a bus on time at an Alicante stop. However, it does not discuss alternatives or when not to use it, such as when the user only wants departure times (next_departures), so it stops short of full exclusion guidance.

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