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

Goes well beyond the annotations (readOnlyHint=false, destructiveHint=false, openWorldHint=true) by disclosing that existing bookings are not touched, that it 'reaches no one' (no notifications), that one call reopens the slot (reversibility), and that it needs the user's Cotlet API key with access to the app. These are exactly the mutation-safety and auth facts an agent needs.

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?

The first two sentences restate the same operation almost verbatim ('Set free spots for start times of an option on one date' / 'Sets free spots per start time for one option and one date'), which is wasted space. The rest is dense and front-loaded, but the redundancy is a clear structural flaw.

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?

No output schema, but the description notes it 'Returns the slots as the app now shows them,' covering the return shape, and it covers auth and mutation side effects. For a 3-parameter mutation this is nearly complete, lacking only explicit routing against sibling availability tools.

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% and the slots schema already shows an example map, so the baseline is 3. The description adds real semantic value by explaining that a value of 0 closes the slot and that it applies per start time for one option/one date, which clarifies the meaning of the map values beyond 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?

States a specific verb+resource: 'Set free spots for start times of an option on one date, or close them with 0.' An agent can tell this mutates per-slot availability. It does not explicitly differentiate itself from the sibling getyourguide_get_availability or getyourguide_update_pricing, so it stops short of a 5.

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?

Implies the two operating modes (set spots vs. '0 closes the slot') and notes it 'runs without asking for your OK,' which is useful invocation context. But it never says when to prefer this over get_availability or update_pricing, so guidance is only implied.

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