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

Annotations already declare readOnlyHint=true, so the description doesn't need to restate safety. It adds useful context about the score's definition (current vs. historical normals) and notes the update cadence ('Updates: on source cadence'), providing freshness expectations beyond what annotations convey.

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 compact and well-structured: it states what it returns, when to call, and update frequency in three logical sentences. Every sentence provides necessary information with no 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?

The description lists return fields and explains the score's meaning, but it never explains how the target county or region is specified, especially since the input schema only has an optional 'days' parameter. The agent is left guessing whether the county comes from conversation context, a default, or some implicit state, which is a critical omission for a county-level tool.

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 only parameter 'days' is thoroughly described in the schema (100% coverage), so the description doesn't need to add more. However, the description's county-level claim is unsupported by any location parameter, and the description fails to clarify how the county is selected, which is a semantic gap that affects invocation.

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 tool returns a 0-100 county-level streamflow stress score based on current gauge-measured discharge vs. historical normals, and enumerates the exact fields returned. However, it does not distinguish this tool from any of the many sibling tools, missing the 'distinguishes from siblings' criterion for a 5.

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 strong when-to-use guidance by citing specific user intents (drought severity, water stress, low river levels, water-supply risk) and even decision contexts (crop lending, facility siting). It lacks mention of alternatives or when not to use, so it cannot earn a 5.

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