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

The destructiveHint=true annotation carries the safety profile, so the bar is lower. The description adds real behavioral context beyond the annotation: the block makes the slot unbookable and is non-recurring. It does not disclose permission requirements, whether an existing appointment on that slot is affected, or any conflict/precondition handling for a mutation.

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 short sentences with no filler, and the core action plus its effect on bookability are front-loaded before the scoping constraints.

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 6-parameter mutation with full schema coverage, no output schema, and a safety annotation present, the description covers purpose, effect, and the one-off constraint adequately. It stops short of prerequisites (permissions, location/staff validity, conflict behavior), which is the only meaningful gap.

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 every parameter (title, reason enum, duration bounds, staff_id URN format, start_time ISO 8601, location_id source) is already documented in the schema. The description restates the location/staff scope but adds no format, default, or interaction detail beyond the schema, so 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 and resource ('Block time on one staff member's calendar at a location') and defines the artifact in concrete terms (a break, meeting or personal time). The clause 'so it cannot be booked' plus 'One-off only' cleanly separates it from the appointment-creation and recurring-schedule tools in the sibling set.

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?

'One-off only' gives an implicit usage boundary (single occurrence, not recurring), which is the extent of the guidance. It never names an alternative or states when NOT to use it (e.g., when an appointment or shift should be created instead), so the agent must infer the choice.

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