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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered. The description adds genuinely useful behavior: the partial-input contract (unspecified fields fall back to site defaults) and the detail flag's effect on the response size. It does not cover runtime/rate considerations, but for a deterministic local model none are expected.

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?

Three tight sentences, front-loaded with what the tool does and what it returns, then the input contract, then the sibling routing. No filler and no repetition of schema detail.

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?

Covers purpose, input convention, output toggling and alternative tools, which is everything an agent needs for a 3-param tool with a fully documented nested schema and an output schema. Nothing material is missing.

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 each input documents units, ranges and defaults, so the schema does the heavy lifting. The description only restates the partial-input convention and the 'yearly' detail mode, both of which the schema already states. Baseline 3 is appropriate.

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 verb+resource+scope: 'Runs one 30-year rent-vs-buy comparison with the rentbuy.org model.' It also enumerates what comes back (winner, net worth at year 30, break-even year), which an agent can use to distinguish it from the batch siblings.

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?

Gives explicit operating instructions ('Give only the inputs you want to change; everything else uses the site defaults') and names the alternatives with the condition for switching: 'Use rentbuy_compare_scenarios or rentbuy_sweep instead of calling this repeatedly.' This is textbook when-to-use routing.

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