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

Annotations already declare destructiveHint=true and readOnlyHint=false, so the safety profile is known. The description adds meaningful context beyond that: a mandatory confirmation workflow, which is real behavioral guidance for a mutation tool. Return shape is covered by the <returns> tag, so this only falls short of 5 by not disclosing reversibility or side effects (e.g., notifications to attendees).

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 summary is two front-loaded sentences with no filler, and the critical confirmation rule is stated directly. The <summary>/<returns> tag wrapper is slightly heavier than needed but not wasteful.

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 destructive update tool, the definition covers the routing prerequisite, the confirmation requirement, and the return summary, while the schema carries full parameter detail. It is essentially complete, though it could note what happens to omitted fields on the existing event.

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 schema fully documents the eight parameters, including local-timezone ISO 8601 rules and the 'only if changing' semantics. The description adds no additional parameter meaning beyond what the schema already provides, so the baseline of 3 is appropriate.

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 states a specific verb and resource ('Update an existing calendar event') and clarifies backend scope ('Outlook or Google Calendar'). It is easily distinguished from siblings like create_calendar_event and search_calendar.

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?

It explicitly names the prerequisite tool ('Use search_calendar first to find the event') and the parameter that requires it ('pass its id here'). It also provides an unambiguous behavioral rule ('ALWAYS present the proposed changes and ask for explicit confirmation'), so when-to-use and alternatives are fully covered.

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