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

Annotations already declare readOnlyHint, destructiveHint=false and idempotentHint=false, so safety is covered; the description adds real behavioral context on top: the default lookahead window, the hard 90-day ceiling, and the timezone rendering (ISO 8601 with offset, text answer in Europe/Berlin). It stops short of describing pagination or what happens when a meeting type has no slots.

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 dense sentences with no filler, and the core resource statement is front-loaded. Slightly telegraphic in the middle (enum recap) but every sentence carries information.

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 an output schema present, return-value documentation is not required, and the description still covers the essentials (timezone of the rendered answer, date window defaults and limits, meeting types and durations). Only minor gaps remain, such as how slot lengths differ per meeting type or any auth requirement.

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 contributes beyond the schema by giving human-readable labels and durations for each enum value ('Kennenlernen, 30 min', 'Sparring, 60 min') and restating the date-range defaults and 90-day cap. These details are not present in the enum alone and materially affect slot interpretation.

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 first sentence names the concrete resource ('free time slots for a call with Jan Linketscher'), which is specific enough to separate it from siblings like book_meeting (which reserves a slot) and list_meeting_types (which returns types, not slots). An agent can identify intent without opening the 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?

Usage is only implied: the tool returns free slots, so an agent can infer it is the precursor to book_meeting. The description never states when to call it, when not to, or names the booking sibling as the follow-up action.

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