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

Annotations already declare it a read-only, closed-world calculation, so the safety profile is covered. The description adds real behavioral value by disclosing the underlying method (Texas Manual on Rainwater Harvesting), the exact formula, and the rounding rule for barrels.

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?

Front-loads the output description, then the method, then formulas — no filler. Slight deduction because 'First flush = roof ÷ 1,000 × 10 gal' hardcodes the default rate rather than referencing the parameter, which reads as a fixed constant.

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 five optional params and no output schema, the description carries the burden well by naming the three returned metrics and the computation path. Minor gaps: no statement that defaults are applied when params are omitted, and no note on units of the returned first-flush value.

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 baseline is 3, but the description goes further by showing how each input enters the math (rain × footprint × 0.62 × efficiency, gallons ÷ barrel size, roof ÷ 1000 × 10), clarifying roles the schema only 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?

Names the exact quantities computed (gallons collectible, barrels filled, first-flush diversion) and the inputs driving them, which separates it cleanly from neighbors like calc_gutter_size or calc_roofing. An agent knows precisely what it gets back.

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?

Implies usage through phrases like 'from a storm, a month or a year of rain,' which hints at the rainfall input, but gives no explicit when-to-use/when-not guidance and never names an alternative calculator for adjacent questions (e.g., gutter sizing).

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