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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description adds genuine context about data provenance (nearest long-record station normals, editorial notes only for roster cities) and the US-only scope, but says nothing about fallback behavior when no station matches.

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?

A single dense sentence with the core value proposition front-loaded and no filler. It is slightly long because it packs three distinct outputs into one clause, but nothing is wasted.

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?

With no output schema, the description usefully enumerates what comes back (normals comparison, records, 5-day outlook, editorial notes). Given only three loosely constrained parameters, it covers most of what an agent needs, though the lack of sibling routing is a residual gap.

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 100% and already documents lat/lon ranges and the roster-city alternative, so the baseline is 3. The description's '(for roster cities) Anecast's editorial notes' adds a small amount of meaning to the city parameter but no syntax or format detail.

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 resource (weather at a US location today) and enumerates the content it surfaces: forecast vs long-record normals/records, 5-day outlook, and editorial notes. It is distinguishable from a plain forecast, though it never draws an explicit line against siblings like what_changed or why_this_forecast.

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?

There is no when-to-use or when-not-to-use guidance beyond an implicit 'anomaly/highlight' framing. With four overlapping siblings (forecast, history_today, what_changed, why_this_forecast), the agent is left to infer which tool answers a given question.

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