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

Annotations only declare readOnly and openWorld; the description contributes real behavioral context beyond that: partial failure semantics ("a part that fails comes back under errors while the others still answer") and the quota-relevant fact that it counts as one request regardless of how many parts are requested. It also caps results at 5 stations/gauges. A minor gap is that it doesn't state cost/latency implications of large include lists, but the essential traits are covered.

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?

Front-loaded with the one-call promise, then a compact per-part enumeration, then the fallback routing rules. Every clause carries information, though the middle run-on segment is dense enough to be harder to scan than a short bulleted structure would be.

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 seven-parameter aggregator with no output schema, the description carries the return-value burden itself by naming the keys each part produces, plus error handling and request accounting. Nothing an agent needs in order to call it correctly and interpret the response is missing.

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 is 3, but the description adds meaning the schema does not: the answer has one key per entry in include, days controls both hourly forecast and daily summaries, hours scopes the air forecast from now, and radiusKm applies specifically to airStations and rivers. It grounds the enums in observable output behavior rather than just repeating field names.

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 ("Everything about one point in one call") and enumerates exactly what the seven include parts return, so the agent knows the payload shape without opening the schema. Sibling tools are named with their narrower scopes (where_is, weather_forecast, air_quality, area_report, route_report), making it separable from all of them.

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?

Explicit routing rules: use where_is when only name and time zone are needed, weather_forecast or air_quality for a single topic with more options, area_report for a region, route_report for a line. That is a genuine when-to-use/when-not matrix rather than implied guidance.

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