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

The annotation readOnlyHint=true already establishes the safe read-only nature, so the description's main additional value is the list of returned fields (id, name, primary flag, access role, timezone) and the cross-account scope. This is meaningful because there is no output schema, but it stops short of describing pagination or edge cases for accounts that are not calendar-capable. With annotations covering the safety profile, the added return-value detail earns a 4.

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, front-loaded with the core action and immediately followed by the usage workflow. Every clause earns its place: the resource, the disambiguation from events, the returned fields, the account scope, and the downstream tools. No filler or repetition.

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 list tool with one fully documented parameter and no output schema, the description is complete: it states the resource, output fields, account scope, and the exact follow-up tools that consume the result. Annotations cover the safety profile, so no material information 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 the single accounts parameter is already fully documented in the schema, including the instruction to omit it for all calendar-capable accounts. The description adds the phrase 'across calendar-capable connected accounts' but no additional syntax, format, or behavior beyond what the schema provides. A baseline 3 is appropriate 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?

The description gives a specific verb and resource ('List the user's Google Calendars') and immediately disambiguates from the nearest sibling by saying '(not events)'. It also enumerates the returned fields (id, name, primary flag, access role, timezone) and the account scope, so an agent can identify exactly what this tool does 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?

The description explicitly states when to use it: 'Use this to discover non-primary calendar_id values before calling list_calendar_events / create_calendar_event / get_event with a specific calendar.' It names the downstream sibling tools that need the discovered calendar_id, leaving no ambiguity about the workflow. The '(not events)' clause further distinguishes it from event-listing alternatives.

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