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

Annotations already declare readOnly, idempotent, non-destructive, closed-world, so the burden is light. The description still adds real behavioral context: times are in America/New_York, each window carries a readable label, a request takes exactly three windows, and the not-bookable branch returns bookable=false plus a page_url. It doesn't cover pagination or the number of windows returned per date range, so not a full 5.

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 short sentences, front-loaded with the primary behavior and the return shape, with the exception path last. Slight vagueness in 'readable label' and the clipped 'A request takes three windows.' keep it from a 5, 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?

There is no output schema, so the description must convey the return shape, and it does: start/end times with timezone, a label, plus the bookable/page_url failure shape. Combined with 100% schema coverage on inputs and read-only annotations, an agent has enough to call it correctly; only the volume/format of returned windows is left implicit.

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 town, trade, and from_date are already documented in the schema, including the YYYY-MM-DD format and the 'earlier days are left out' semantics for from_date. The description only restates trade and town as the lookup key and adds no syntax or format detail beyond the schema, so the baseline 3 applies.

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 (return) and resource (visit windows) plus the scope (per trade and town), and distinguishes itself from the sibling get_coverage by naming it as the precondition. An agent can pick this tool over find_contractors/start_booking without opening a 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 explicitly gates usage on get_coverage saying 'bookable' and names the alternative path when it is not: bookable=false and page_url is where to send the homeowner. This is clear when-to-use and when-not-to-use guidance referencing a sibling.

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