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

Annotations already declare readOnlyHint=false, destructiveHint=true, idempotentHint=true, and openWorldHint=true. The description adds meaningful details beyond those: a concrete destructive effect ('Making a sub-calendar inactive hides it from users without admin rights'), the permission requirement, and partial-update semantics. It stops short of explaining all destructive consequences or error behavior, so 4 is appropriate.

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?

The description is four tight sentences, front-loaded with 'WRITE:' and the core action. Every clause earns its place: what changes, partial-update semantics, permission need, destructive side effect, and endpoint. There is no filler.

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 an update tool with no output schema and five parameters, the description covers the essential behavioral context: write intent, partial update, admin permission, a destructive side effect, and the HTTP method/path. It does not mention error behavior or return values, but with no output schema the latter is not required. The coverage is strong but not exhaustive.

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 only 20%, so the description must carry more weight. It names the four updatable fields (name, color, overlap rule, active state), which maps to the optional parameters, and clarifies partial-update behavior. However, it adds no format or constraint details beyond what the schema already enforces numerically (e.g., color range 1-48, name length), so it only partially compensates for the low coverage.

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 states a specific verb and resource ('change a sub-calendar's name, color, overlap rule or active state') and clearly distinguishes it from sibling tools like create_subcalendar or update_event. An agent can immediately tell this is the partial-update tool for an existing sub-calendar.

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?

It gives clear context for use: 'WRITE' marks it as a mutation, 'fields you leave out keep their value' describes the partial-update behavior, and 'Needs admin permission' sets a prerequisite. It does not name alternative tools or state when not to use it, so it falls short of a 5.

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