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

Annotations cover safety (readOnly, idempotent, non-destructive), but the description adds behavior well beyond them: chronological ordering, decoded output, a defined summary payload, the 400-report API ceiling (~8 days at half-hourly stations), the 30-day maximum, and a 1-credit cost. That operational envelope is exactly what an agent needs to size a request correctly.

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 core statement, then supporting detail in descending priority; every clause (source, cap, exclusion, cost) carries information. It is dense but not padded, though the summary enumeration mid-description is slightly long-winded.

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?

No output schema exists, yet the description explains what comes back: every observation oldest first plus an aggregate summary (high/low temperature, strongest gust, flight-category low, reported weather). Combined with the cap and cost disclosure, an agent can call this correctly without further information.

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% and each parameter already documents its type, range, and default, including the note that the summary covers the whole window regardless of limit. The description only restates the hours window ('over the last N hours') and the 30-day bound, adding nothing about interaction between hours and limit. Baseline 3 applies.

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+scope: 'Every METAR observation for one airport over the last N hours', plus ordering (oldest first) and a summary payload. The 'what actually happened' framing and the reference to a named upstream source (NOAA/NWS Aviation Weather Center) make the historical-observation role unambiguous against forecast-oriented siblings like taf_forecast.

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?

Gives a clear when-to-use scenario ('checking what actually happened at a station: rain, gusts, fog, when it cleared') and an explicit exclusion ('not for flight planning'). It does not name the sibling tools it competes with (metar_latest, taf_forecast, pireps_near_airport), so the routing signal is implicit rather than explicit.

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