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

Annotations already cover safety (readOnly, idempotent, non-destructive, openWorld), and the description still adds real behavioral context: the ~7-day horizon, that the tool admits rather than guesses beyond it, and that a bare hour without AM/PM is refused instead of inferred. This is exactly the kind of guardrail behavior an agent needs.

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-loads the purpose with illustrative phrasing, then moves to parameters, return shape, and the horizon limit. The example phrases cost a little space but earn it by clarifying accepted time formats; overall tight and well-ordered.

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, so the description carries the burden of describing returns and it does so (one-line summary, temperature range, rain, wind, actionable conditions, hourly and daily rows). Combined with the horizon caveat and time-format guidance, an agent has everything needed to call it correctly.

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 value by specifying the intended invocation pattern (start_time required in practice, end_time or duration_hours as optional alternatives). It complements rather than repeats the rich per-parameter schema text.

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 (forecast over a time period) and illustrates scope with concrete query examples ('this weekend', 'between 6 PM and midnight'). It implies a distinction from the current-conditions sibling get_weather via the time-range framing, but never names an alternative explicitly.

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 clear context for invocation ('What's Saturday looking like?', 'this weekend') and tells the agent the canonical call shape: give start_time, optionally end_time or duration_hours. It stops short of naming when to prefer sibling tools like find_best_weather_window or get_trail_weather.

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