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

Annotations already declare read-only/idempotent/non-destructive, and the description goes well beyond them: pricing (0.01 USDC via x402 or 5 credits), the free tier (first 5 paid-tool calls/day, no payment or key), and the qualitative caveat that results are an estimate with a link to the official check. Those are exactly the facts an agent needs before deciding to spend money.

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-loaded with the trigger sentence and dense but non-redundant: segment thresholds, pricing, and free tier each earn their place. The final two sentences on payment could be tightened, but there is no filler.

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?

Even without an output schema, the description says what comes back (points, likely segment, max basic rent, official-check link) and what input drives it. For a paid, read-only estimator with full schema coverage, nothing an agent needs before invoking 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%, so the schema already documents postcode, house_number, addition, house_letter, q and api_key in more detail than the description does. The description's "Input: postcode + house number" adds the primary pair but omits that q is a free-text alternative and that api_key is the credit-based auth path, so it adds little beyond, and slightly narrows, the schema.

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 a specific verb+resource (estimated rent points / WWS) and enumerates the actual outputs: points from floor area, energy label and neighbourhood WOZ, segment thresholds (143/144-186/187+), and approximate max basic rent. No sibling tool (address, energy, crime, house prices) does rent-point calculation, so the boundary is unambiguous.

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?

"Use when a tenant asks if their Dutch rent is too high or what the maximum rent is" gives a concrete triggering scenario, and "An estimate with a link to the official check" sets the accuracy boundary. It stops short of naming a sibling to use instead when the question is really about energy label or WOZ value alone, so no explicit alternatives or exclusions.

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