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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), and the description adds substantial non-obvious behavior: the available window is weekdays 10:00–17:00 London time, at least 24 hours ahead and at most four weeks out. It also discloses the return format (ISO 8601 with Europe/London offset), which annotations cannot express.

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?

One dense but well-ordered passage: workflow position first, then what it returns, then the scheduling constraints, then the optional parameters. No sentence is redundant given how much specification it carries.

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 no output schema, the description correctly shoulders the burden of describing return values and all business constraints, which it does. It omits what happens when no slots match (empty result) and any cap on the number of times returned, which an agent might reasonably need.

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 the baseline is 3, but the description adds genuine meaning the schema lacks: from and to are interpreted as 'London days' that narrow the range, tying the date parameters to the same timezone as the returned times. It adds interpretation but no new syntax or edge-case behavior.

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 resource and scope — 'Free start times for a meeting type, from Patrick's live calendar' — plus its position in the workflow ('Step 2 of the booking guide'). An agent can distinguish it immediately from list_meeting_types (enumerates types) and book_meeting (consumes the slots this returns).

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?

The 'Step 2 of the booking guide' reference gives clear sequencing context and the from/to sentence explains how to narrow the search. It never states an explicit when-not-to-use case or names a sibling alternative if the requested window is empty, so it stops short of a 5.

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