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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint, so safety is covered without the text. The description does add two genuinely behavioral facts beyond that: the UK-time 'tomorrow' default and, importantly, the semantics of an empty result, which prevents the agent from wrongly concluding a property is unviewable. It still says nothing about how many slots may return or what a slot entry looks like, so it stops short of rich disclosure.

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 core purpose is front-loaded in the first clause and the second sentence, though longer, carries the single most decision-relevant caveat. The em-dash construction makes the empty-list case slightly dense to parse but nothing is redundant.

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?

For a two-parameter read tool with no output schema, the definition covers purpose, the one parameter default that matters, and the failure-mode interpretation of an empty result. It is nearly complete; the only omission is any hint of what a returned slot contains beyond being 'open'.

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 schema already documents both the YYYY-MM-DD pattern with the tomorrow/UK-time default and that property_id comes from search_properties results. The description restates the date default without adding format or sizing detail, 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 (List) plus a precisely bounded resource: pre-scheduled viewing slots still open, for one property, on one date. The scope qualifier 'pre-scheduled' immediately distinguishes it from book_viewing, which handles ad-hoc requests.

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?

Explicitly names the alternative and the condition that selects it: if the list is empty, use book_viewing with preferred days/times, because that works for every listing. That is a concrete when-to-use-this vs when-to-use-sibling rule rather than an implied one.

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