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

Annotations declare readOnlyHint=true, so the tool is known to be safe and non-mutating. The description adds the information that two output modes exist (named 12-hour periods or hourly), but this is already fully documented in the 'hourly' parameter schema. Since the description contributes little beyond what annotations and schema already convey, a score of 3 is appropriate.

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-formed sentence that front-loads the primary purpose and immediately follows with the key behavioral distinction (two output formats). Every word carries meaning, with no filler or redundancy.

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 that the schema fully documents parameters, the output schema exists, and the read-only annotation is present, the description is sufficient for an agent to invoke the tool correctly. The only minor gap is that it does not explain pagination behavior, but that is handled in the cursor parameter description, so completeness is good. A slight deduction for the lack of any mention of how to handle the hourly vs named-period choice in 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?

The schema provides 100% description coverage for all four parameters, including format details for latitude/longitude and the meaning of 'hourly' and 'cursor'. The description does not add any new parameter context beyond what the schema already states, so the baseline of 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?

The description clearly states the action ('Get the weather forecast') and the resource ('a US location'), and it adds the distinguishing detail of returning either 12-hour named periods or hourly breakdowns. This makes the tool's purpose explicit and differentiates it from sibling tools like observations or office discussion without ambiguity.

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 provides no guidance on when to use this tool versus alternatives such as nws_get_zone_forecast or nws_get_observations. It does not mention any exclusions, prerequisites, or hints about choosing between forecast modes. An agent must infer usage context from external knowledge, which is a significant gap given the sibling toolset.

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