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

Annotations already declare readOnlyHint=true, destructiveHint=false, openWorldHint=false, so the safety profile is covered. The description adds a genuine behavioral constraint beyond that: calendars outside the caller's access are not returned, and omitting the id changes downstream tool behavior. Pagination/return shape is still unstated, keeping it below a 5.

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?

Three short sentences, no redundancy, with the core action and the highest-value guidance (where the calendarId comes from) front-loaded before the access-scope caveat.

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 read-only, single-parameter list tool with annotations covering safety and no output schema, the description covers everything an agent needs: what it lists, when to call it, what it returns that matters (calendarId), and what is filtered out.

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?

Only one parameter (mailbox) with 100% schema coverage, so the schema already carries the description and its pointer to list_authorized_mailboxes. The description references calendarId, but that is an output value rather than the input parameter, so it adds little parameter-level meaning. Baseline 3 applies.

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 (List) and resource (Outlook/Microsoft 365 calendars) scoped to one account, which cleanly separates it from list_google_calendars and from the create/delete/rename Outlook calendar siblings.

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?

"Start here to get the calendarId the event tools take" gives explicit sequencing guidance, and the follow-on clause explains the consequence of omission (event tools fall back to the default calendar). This is a real when-to-use rule rather than an implied one.

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