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

Annotations already indicate readOnlyHint=true, so no further safety disclosure is needed. The description adds behavioral context beyond the annotation by detailing the response contents (per-day high/low, precipitation chance, max wind, conditions) and the forecast range, which helps the agent set expectations without needing to inspect the output schema.

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 compact and well-structured: it starts with the core purpose and output, then gives usage guidance with examples, and ends with a parameter clarification. Every sentence contributes—no filler, repeated schema information, or unnecessary detail.

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?

Given the simple two-parameter schema and the presence of an output schema, the description is complete. It explains what the tool returns, when to use it, how to interpret the 'days' parameter, and the default behavior. There are no significant gaps for an agent to invoke this tool 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 description coverage is 0%, but the description compensates well for the 'days' parameter by specifying 'how many days ahead (1-7, default 5)'. The 'city' parameter is not explicitly defined, but the examples ('Paris', 'Bangkok') and the phrase 'for a city' make its meaning immediately clear, so the description adds sufficient semantic value beyond the raw schema.

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 clearly states this is a 'Daily weather forecast for a city' with a defined scope ('up to 7 days ahead') and specific output fields (high/low, precipitation chance, wind, conditions). It distinguishes itself from sibling 'get_weather' by emphasizing forward-looking, future weather questions rather than current conditions.

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 description explicitly says 'Use for forward-looking questions' and provides concrete examples ('will it rain in Paris this weekend?', 'what's the weather in Bangkok next week?', packing/trip-planning). It does not name the alternative 'get_weather' or state when not to use it, but the guidance clearly implies a contrast with current-weather use.

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