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

Annotations already declare a non-read-only, non-destructive, open-world mutation, so the safety profile is largely covered. The description adds genuine behavioral value the annotations do not: the ordered GET-overlay-PUT sequence, the semantics of `null` as a field clear, and a lost-update race warning ('concurrent callers can clobber each other').

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?

Content is largely relevant, but the delivery is dense and awkward: a stray 'resolves to `null`', backticked type signatures, and semicolon-packed clauses make it read like an implementation note rather than a tool description. It is front-loaded with the core operation, which partly offsets the stuffing.

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 mutation tool with no output schema and a nested-object parameter, the description covers the mechanism, the null-clear semantics, and the concurrency hazard, and it states the return resolves to null. It omits error/auth conditions (e.g., behavior on an unknown eventId), which is a minor 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 coverage is only 50% (nested `changes` fields are mostly undocumented beyond `date` and `eventId`). The description compensates by enumerating the overlayable fields and, crucially, defining the `null`-clears-an-optional-field semantics that the schema does not express. This is meaningful added value beyond the raw property list.

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?

The description clearly states this is a read-modify-write update of a stored calendar event and names the resource (event). It is unambiguous as to verb+resource, though it does not explicitly contrast itself with siblings like create_calendar_event, get_calendar_event, or list_calendar_events.

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?

There is no explicit when-to-use or when-not-to-use guidance and no mention of alternative tools for the same resource (create/delete/get calendar event). The only usage hint is the parameter-level note that `null` clears an optional field, which is not routing guidance.

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