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

While annotations already declare readOnlyHint=true, the description adds substantial behavioral context: defaults to today and the user's city, returns a compact day overview plus part-of-day breakdown (not an hourly dump), and mentions the ~16-day coverage limit. This goes well beyond the structured annotations and helps the agent set expectations.

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 a single well-structured paragraph that front-loads purpose, then usage, parameters, and return format in logical order. Every sentence earns its place—no fluff, no repetition—and it remains readable despite being thorough.

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 simple 2-parameter read-only tool with no output schema, the description covers purpose, usage boundaries, parameter semantics, defaults, and output shape. Nothing an agent needs to call it correctly is missing, and the sibling differentiation adds critical routing context.

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%, yet the description still enriches both parameters: date gets ISO format, default-to-today, and coverage range; location gets example values and default-to-saved-city behavior. This clarifies usage beyond the schema's bare definitions, making parameter semantics exceptionally clear.

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 states a specific verb (get), resource (weather forecast), and scope (for a day), and explicitly distinguishes it from get_schedule and show_day by noting they only provide a one-line headline. An agent can immediately understand what this tool does and how it differs from siblings.

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?

Provides explicit when-to-use (outdoor/weather-sensitive plans, explicit user request) and when-not-to-use (indoor plans), plus names specific alternatives (get_schedule, show_day) for quick glances. The condition for choosing this tool—needing hourly detail like the dry/daylight window—is clearly stated, leaving no ambiguity.

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