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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered. The description adds real behavioral context beyond that: the 14-day span limit, the fact that results are ISO 8601 with offsets, and the guarantee that only open (never busy) times are returned. With no output schema, the return-format note is valuable, though it stays brief.

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?

Front-loads the core purpose, then covers the `windows` option and return format in short sentences. Slightly redundant — 'Only open times are ever shown' overlaps with the opening sentence and with the schema's own wording — but nothing is bloated.

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 4-parameter availability-lookup tool with a 100%-covered schema, the description supplies the key framing (open starts, optional calendar intersection) and a brief return-format note. Since no output schema exists, the terse return description leaves a little unexplored, but it is sufficient to call the tool correctly.

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 the schema already documents `from`, `to`, `items`, and `windows` in detail. The description's mention of `windows` largely restates the schema's own explanation, adding little new syntax or constraint detail. Baseline 3 when the schema does the heavy lifting.

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 ('Find the start times that are open') scoped to 'what is being booked' between two dates. This is clearly distinguishable from the sibling book/get_booking tools, which act on existing bookings rather than surfacing availability.

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?

Explains the central usage decision: pass `windows` to intersect with the customer's calendar, or omit it to see every open start. It does not explicitly name siblings (e.g., 'use this before book'), but the when-to-supply-windows guidance is clear and actionable.

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