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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description's only behavioral addition is the multi-account requirement for `account` — which largely restates the schema — and it says nothing about return shape, error behavior for a missing/stale id, or default calendar resolution.

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?

Two tight sentences: the identity/scope of the operation is front-loaded, and the conditional account guidance follows. No redundant or filler clauses.

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 simple read-only getter with no output schema, the description covers what the agent needs to call it correctly: the id source and the account condition. Minor gaps remain around failure modes when an id is not found, but nothing essential is missing.

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 all three parameters are already documented, including the same multi-account condition for `account`. The description adds provenance for `event_id` but no syntax, format, or fallback detail beyond the schema, so the 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 and resource ('Fetch one Google Calendar event by id'), explicitly scoping to a single event, which distinguishes it from the sibling list_calendar_events. It also names the origin of the id, so the agent knows exactly which tool to call before or after this one.

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?

Gives clear context for use: fetch a single event whose event_id came from list_calendar_events or search results, and pass account when multiple calendar-capable accounts exist. It does not explicitly exclude or route against related siblings like update_event, respond_to_event, or delete_event, but the read-only single-record framing makes the boundary clear.

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