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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the description's 'read-only, does not change anything' largely reinforces structured data. It still adds real context the annotations cannot express: that coverage may fail for a given postcode, and that results include arrival windows plus hourly rates in GBP for a bounded N-day horizon.

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 core capability, followed immediately by the usage rule and the read-only guarantee. No filler and nothing buried at the end.

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 only two simple parameters, full schema coverage, and rich annotations, the definition is complete. Even though no output schema exists, the description explains what comes back — a coverage determination and bookable windows with hourly rates — which is exactly what an agent needs to plan the following book_plumber call.

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 both the postcode format and the 1–21 day range are already documented in the schema. The description only restates 'postcode' and 'next N days' in prose, adding no formatting, defaulting, or edge-case detail beyond what is already structured.

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 and resource — checking postcode coverage and listing bookable arrival windows with hourly GBP rates over N days — and pairs it with a clear negative scope ('it does not book a visit'). An agent can distinguish this from book_plumber, quote_installation, and order_installation without opening any schema.

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 gives an explicit sequencing rule, 'Use this before book_plumber,' which is the primary dependency an agent needs. It does not address when an agent should skip this check in favour of quote_installation or order_installation, so the routing guidance is clear but not exhaustive.

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