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

Annotations already establish read-only, non-destructive behavior, and the description adds meaningful context beyond them: vessel-based lookups use the last known position, current conditions are the default mode, and each returned weather field has a matching entry in a *_units object. This helps the agent interpret and use results without contradicting annotations.

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 four tightly packed sentences: output scope first, then location resolution, then mode selection, then units. Every sentence carries operational information, and there is no filler or repetition of the schema.

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 an output schema exists and all parameters have schema descriptions, the tool description sufficiently covers location disambiguation, default mode, alternative forecast modes, and output unit behavior. An agent has everything needed to select and invoke the 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?

The schema already documents all 8 parameters, so the baseline is 3. The description adds value above the schema by imposing the 'exactly one of' cross-parameter constraint and by explaining the units-object relationship, which is not derivable from individual parameter descriptions.

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 opens with a specific verb and resource ('Return weather for one location') and enumerates the marine and atmospheric fields returned, so an agent knows exactly what the tool does. The scope ('one location') also separates it from vessel, port, and history tools among 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?

It clearly instructs how to specify a location ('exactly one of: coordinates ... a vessel ... or a port') and how to choose current, daily, hourly, or combined modes. It provides strong context but does not explicitly enumerate when not to use this tool versus sibling tools, though sibling names make that largely unnecessary.

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