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

readOnlyHint=true already tells the agent this is a safe read with nothing destroyed, so the bar is lower. The description's only added behavioral context is the REST mapping (GET /calendars), which is useful for API-parity and debugging but says nothing about result size, pagination, or whether inactive calendars are included.

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 short, front-loaded sentences with no filler: the purpose statement comes first and the REST endpoint follows as a compact reference. Every element earns its place.

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 zero-parameter read tool with readOnlyHint and an empty schema, the definition is essentially sufficient. The only minor gap is that no output schema exists and the description doesn't describe the shape of a returned calendar (id, name), which would help an agent chain into booking calls.

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?

The tool takes zero parameters, so the baseline is 4. There is no parameter behavior the description could add, and the schema is trivially complete; nothing is missing here.

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 the account's calendars') and adds a parenthetical that defines what a calendar is in this domain (staff/resources appointments can be booked on), which disambiguates it from siblings like acuity_list_appointment_types or acuity_list_appointments. It does not explicitly name a sibling it should not be confused with, so it stops short of a 5.

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 parenthetical 'appointments can be booked on' hints at why an agent would list calendars (to find bookable staff/resource IDs), but there is no explicit when-to-use, when-not-to-use, or alternative named. Usage is only implied from the resource semantics.

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