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

Annotations declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description goes beyond that by publishing the exact formulas used for both the raise and dilution paths, which is genuinely useful behavioral disclosure for a deterministic calculator. It stops short of noting edge behavior (e.g., what happens when current <= target in the drain formula, or that the result is expressed in ounces/gallons).

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?

Two sentences, front-loaded with the outcome and then the supporting formulas; nothing is wasted. The formula notation ('÷ 10 × gallons ÷ 10,000 × 13') is dense and slightly hard to parse, but it is compact rather than padded.

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 should clarify what is returned; it implies ounces of stabilizer and gallons to drain but never states the output units or result shape explicitly. Defaults (target 40, current 0, 15000 gal, fill 0) live only in the schema, and the no-op case for lowering is unaddressed, leaving modest gaps for an agent relying on the description alone.

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 100%, so the baseline is 3. The description adds value by showing how each input participates in the math — current and target in the raise formula, fill_water_ppm specifically as the dilution denominator alongside pool_gallons — giving the agent a functional understanding of the parameters beyond their schema labels.

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 verb+resource pair (raise cyanuric acid by adding stabilizer, or lower it by draining/refilling) and scopes it precisely to CYA. Among the many calc_pool_* siblings (alkalinity, chlorine, salt, calcium hardness), this is unambiguously the stabilizer/CYA one.

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 frames the two operating modes (raise to target vs. dilute down to target), which tells the agent the tool's two use cases. However, it never names a sibling alternative or states a condition for choosing this tool over calc_pool_alkalinity or calc_pool_volume, so routing guidance is only implied.

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