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

Goes well beyond the annotations: it spells out patch semantics (omitted fields stay), which mutations are externally visible and can propagate to calendar-feed subscribers, and that the operation is not undoable because no previous values are retained. The annotations flag destructiveHint/idempotentHint generically; the description explains the actual blast radius.

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?

Front-loaded with the operation type and scope, then risk, then the endpoint. Every sentence carries distinct information and nothing is padded.

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 10-param mutation with a nested custom_data object and no output schema, it covers the essentials an agent needs (what changes, what stays, what leaks publicly, irreversibility) and the annotations cover the safety profile. It remains thin on the nested custom_data semantics and the template-id fields.

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?

With 60% schema coverage across 10 params, the description adds meaningful semantics: the partial-update rule tells the agent that any parameter it omits is preserved, which is the key behavioral fact for a 10-field PATCH. It also groups title/description/timezone as publicly visible, though it says nothing about custom_data, weekday_begin, or the template-id fields.

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?

Opens with an explicit WRITE marker and a specific verb+resource ('changes fields of an existing calendar'), and the partial-update scope is stated immediately. It is unambiguously distinct from the sibling create_calendar and update_event tools.

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?

Gives a clear prerequisite ('read the calendar first' because prior values are not kept), which routes the agent to the get_calendar sibling. It does not state when NOT to use this tool or name an alternative for related-but-different operations, so it falls short of full when/when-not guidance.

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