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

Annotations already declare readOnly=false, openWorld=false, idempotent=true and destructive=true, so the safety profile is covered structurally. The description adds only the scoping fact that the mark applies to the authenticated user; it says nothing about what destructiveHint actually destroys here (e.g. overwriting an existing mark for that date), so it adds some but not rich behavioral context.

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 zero filler: the action and scope come first, followed by the two argument formats. Nothing is redundant or 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 two-parameter mutation tool with a full schema, complete annotations, and an output schema (so return values need not be described), the description is close to sufficient. The only material gap is that a destructive-marking operation never explains what an existing entry for the same date would be replaced by.

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%, so both parameters are already documented, and the description merely restates them ('date is YYYY-MM-DD', 'event is flowstart or flowend'). No syntax, mutex, or dating-rule semantics are added beyond the schema, so the baseline 3 applies.

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: 'Mark a menstrual-cycle start or end for the authenticated user', which is unambiguous about what the tool writes. It does not, however, differentiate itself from the related siblings delete_flow or get_flows, so an agent must infer the boundary from names alone.

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?

There is no when-to-use guidance, no prerequisite or ordering information (e.g. whether a start must precede an end, or how this interacts with get_flows), and no named alternative. The description is purely declarative.

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