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 adds real value beyond that: the visibility scope ('all calendars the authenticated account can see'), the returned field set (id, name, profile, readonly, primary), and the backing endpoint. With no output schema, naming the fields is the main source of behavioral detail, though it says nothing about pagination or result size.

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?

A single front-loaded sentence plus the endpoint annotation, with no filler or repetition. Every element carries 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?

For a zero-parameter read tool with no output schema, the definition supplies the scope, the returned fields, and the endpoint, which is enough for correct invocation. It stops short of five because nothing is said about result volume or ordering when an account has many calendars.

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 there is nothing for the description to disambiguate; the baseline for a parameterless tool is 4. The parenthetical is a return-value list, not parameter documentation, so it neither adds nor detracts 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 all calendars') and scopes it to 'the authenticated account can see', so an agent knows exactly what the call returns. It does not explicitly distinguish itself from the closest sibling, cronofy_list_profiles, but the resource noun is unambiguous.

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?

No when-to-use guidance, no prerequisites, and no mention of alternatives such as cronofy_list_profiles or cronofy_get_account. Usage is only inferable from the resource name, which is the minimum level of implication.

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