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

readOnlyHint=true already declares this is a safe read, so the safety profile is covered by annotations. The description adds genuine value beyond that: it lists the returned attributes and discloses the critical behavioral interaction that update_event replaces attendees wholesale. It does not mention pagination, but for a single-event attendee list that's minor.

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 sentences with no waste. The field list is front-loaded, and the usage condition with the sibling alternative follows. Every sentence carries distinct information.

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?

With no output schema, the description compensates by enumerating the returned fields and RSVP status values, and it covers the key usage rationale. Nothing an agent needs to call this correctly 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 in the schema, including the `account` conditional. The description restates the account guidance ('Pass `account` when more than one calendar-capable account is connected') without adding syntax or format beyond the schema. Baseline 3 when the schema does the heavy lifting.

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 ('List one Google Calendar event's attendees') and enumerates the exact fields returned (email, display name, RSVP status, organizer flag, self flag), distinguishing it from sibling list tools. An agent can identify the operation without opening the schema.

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?

Explicitly says to use this 'before update_event when you want to add/remove attendees while keeping the existing ones', and explains why — that update_event's attendees field replaces the list wholesale. This names the alternative and the condition that selects this tool.

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