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

Annotations already carry idempotentHint=true, destructiveHint=false, and readOnlyHint=false. The description adds only the authenticated-user scope and the allowed event values, which are already present in the schema. It does not explain whether marking an existing date overwrites a prior flow or how repeated calls behave, though the idempotent hint partially mitigates this.

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 two short sentences: the core action is front-loaded, followed by a compact parameter summary. It contains no filler and each sentence 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?

The description plus schema fully cover the two required parameters, and annotations/output schema cover safety and return values. The only meaningful gap is a brief note on how a new flowstart/flowend relates to an existing flow record, but this is a nuance rather than a blocker for correct invocation.

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%, and the description simply restates 'date is YYYY-MM-DD' and 'event is flowstart or flowend.' No additional parameter semantics, constraints, or examples are provided beyond what the schema already declares.

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 uses a concrete verb ('Mark'), names the resource ('menstrual-cycle start or end'), and scopes it to the authenticated user. It clearly differentiates from sibling tools like create_event (generic calendar event) and delete_flow/get_flows (flow lifecycle operations).

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 implies the tool is for recording flow boundaries and correctly restricts event values to flowstart/flowend. However, it does not explicitly say when to choose this over create_event/update_event or state what not to use it for, leaving usage largely inferred from the title and sibling tool names.

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