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

Annotations already declare idempotent=true, destructive=true and readOnly=false, so the safety profile is covered. The description adds genuinely non-structured behavior: unspecified fields are left untouched, null clears a field, null does NOT clear receiving, and time_zone only takes effect with zoneConfirmed true. It does not mention permission requirements or error behavior.

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 general partial-update rule is correctly front-loaded, and each clause covers a distinct behavior that earns its place. However, the two comma-spliced run-on sentences are dense and force the agent to re-parse to separate the rules for calendar, receiving and time_zone.

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 19-parameter, zero-required, no-output-schema mutation tool, the description covers the highest-risk semantics (partial update, null clearing, the receiving exception, the time_zone gate). The remaining hours/horizon/buffer fields are adequately handled by the 89%-covered schema, so nothing critical is missing.

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 89%, so baseline is 3, but the description meaningfully exceeds the schema for calendar ('marks one calendar ... as counting as busy or not'), receiving (the calendar bookings are made in, and exempt from null-clearing) and time_zone (gated on zoneConfirmed). Those are cross-field semantics the schema does not express, since most schema descriptions are only form examples.

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: 'Change any of the person's scheduling preferences', and cross-references preferences_get as the source of field names, which implicitly separates it from the read sibling. It does not explicitly name other write siblings such as busy_everywhere_set or booking_page_set, so routing is inferred rather than stated.

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 implied by 'Change any of the person's scheduling preferences ... the rest left as they stand', which tells the agent this is a partial-update path and that calling preferences_get first is how field names are learned. There is no explicit when-not guidance or comparison against alternative write tools like busy_everywhere_set.

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