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

The description adds real behavior beyond the annotations: partial update by default, 'null clears one', the exception that receiving's null does not clear, and the confirmation gate on time_zone. Against an annotation set that already declares destructive/idempotent/readOnly, this is meaningful added context. It leaves unstated whether changes are reversible or whether the caller must obtain user confirmation for destructive overrides.

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?

It is compact for a 19-parameter mutation and the core semantics are front-loaded in the first clause. But it is written as a dense run-on of comma-and-semicolon clauses, so a reader must untangle quoted-sounding names like 'receiving, which null does not clear' from the grammar of the sentence. Structure costs more than it should for the length.

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-param, nested-object mutation with no output schema, the description covers the decision-relevant edges: partial update, null clearing with one exception, calendar busy flagging, receiving-calendar restrictions, and the time_zone confirmation gate. Gaps remain around whether an empty call is a no-op and what errors to expect, but the agent has enough to call it 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?

With 19 parameters and 89% schema description coverage, the schema carries most semantics, so the baseline is 3. The description does add genuinely non-obvious semantics for the two nested objects (calendar = busy/counting flag; receiving = the booking calendar, and only a server that sends invitations itself) and the zoneConfirmed linkage, which pushes toward a 4. However, the many scalar preferences (hours, buffers, limits) are not addressed at all beyond 'the rest left as they stand'.

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 ('Change any of the person's scheduling preferences') and adds partial-update semantics ('the rest left as they stand') that distinguish it from a full replace. It also anchors to the read sibling preferences_get, so the agent knows which tool it is paired with. It loses a point because the phrasing 'as preferences_get names them' is dense and forces a second read to parse.

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 rather than stated: referencing preferences_get hints the read should come first, and the time_zone rule ('changes only with zoneConfirmed true, once the person has confirmed it as theirs') is an explicit conditional. But there is no explicit when-to-use/when-not, no statement about what happens for preferences not listed, and no guidance on confirming changes with the person despite destructiveHint=true.

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