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

Annotations already declare destructive=true, idempotent=true, and openWorld=false, so the safety profile is covered. The description adds real context beyond that: the not-found behavior for missing or non-owned ids, and the waitSync latency/response tradeoff (false responds immediately and links may be absent).

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?

Four tight sentences, front-loaded with purpose and partial-update usage, then date formatting, error behavior, and the sync flag. No repetition of the title and no filler.

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?

An output schema exists, so return values need not be explained. For a 13-parameter mutation tool with destructive/idempotent annotations, the description covers the ownership constraint, the not-found failure mode, and the blocking-vs-immediate sync behavior; only replacement-vs-merge semantics for omitted fields are left implicit.

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 baseline is 3. The description largely restates schema content (start/end ISO 8601 format, waitSync default), though it does sharpen waitSync by stating the immediate-response case may lack links; it says nothing about calendarId, timezone, or rrule semantics.

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 ('Update an event') and adds the ownership scope ('owned by the authenticated user'), which is the key differentiator from siblings like create_event or get_event. It stops short of naming an alternative tool outright, but the resource is unambiguous.

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?

'Pass id plus any fields to change' establishes partial-update usage, which is genuinely useful guidance. However, it never addresses when to use this versus set_event_status (which overlaps on the status field) or delete_event, and gives no prerequisites or exclusions.

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