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

With no annotations, the description carries the behavioral burden and does disclose useful traits: a 25-postal-code limit, sorting with rising sites first, and the returned information. However, it omits important details such as error behavior, authentication expectations beyond the token schema field, and whether results are cached or real-time.

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 definition is a compact single sentence with the key scope and return summary front-loaded after the PRO marker. It is appropriately sized, though the standalone 'PRO.' is slightly opaque and could be clearer.

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 lookup tool with no output schema and no annotations, the description gives enough to understand the basic return (nearest gauge and 24-hour change) and input limit. It remains incomplete on sibling selection, postal code formatting, and fuller response/auth behavior.

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 50%: access_token is documented in the schema, while postal_codes is not. The description partly compensates by stating the 25-postal-code limit and implying the array contains postal codes, but it does not clarify postal code format or validation.

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 resource and scope: nearest gauge and 24-hour level change for up to 25 postal codes, with rising sites first. It distinguishes itself operationally from siblings by being postal-code based, though it does not explicitly name or contrast with gauge_trend or river_levels.

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 gives an input constraint (up to 25 postal codes) and ordering behavior, but does not say when to use this tool instead of gauge_trend or river_levels. There are no exclusions, prerequisites, or alternative-selection guidance beyond the vague PRO marker.

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