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

Annotations already mark this as a mutating, idempotent, non-destructive call. The description adds meaningful behavior beyond that: missing/foreign ids return not found, waitSync controls waiting for the external calendar and whether links are present, and date-time formats for all-day events. No contradiction with annotations.

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 compact sentences, front-loaded with the core action, followed by the most decision-relevant details (date formats, error behavior, sync default). No filler or redundancy.

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 13-parameter mutation tool, the description covers the essential call contract: ownership restriction, patch semantics, date formats, not-found errors, and waitSync behavior. The output schema exists, so return-value details are not required here, and the parameter schema documents the remaining fields.

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 100%, so the baseline is 3. The description adds the partial-update semantics ('Pass id plus any fields to change') and re-emphasizes the start/end ISO/all-day constraint and waitSync consequence, which adds some meaning beyond the schema even though much is duplicated.

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 names a specific operation ('Update'), a specific resource ('an event owned by the authenticated user'), and a clear contract ('Pass id plus any fields to change'). This is distinct from create_event, delete_event, and set_event_status because it scopes to owned events and field-level modification.

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?

The description clearly implies when to use the tool: to modify an existing event the caller owns. However, it never states alternatives or exclusions, such as choosing set_event_status for a status-only change or create_event for new events, leaving sibling routing to inference.

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