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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), but the description adds genuine value: it discloses the return artifact (an .ics with an all-day event, steps and official link), the alert schedule (9am the day before and 9am on the day), and that 'Nothing is stored'. No return format on payload structure beyond that, but that is minor.

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 and informative, with the deliverable and behavior described crisply. The leading 'Cancel My Sub.' restates the app/title and the reminder phrase is repeated from the title, which is minor redundancy but not damaging.

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?

With no output schema, the description correctly carries the burden of describing the return artifact and its contents, and it does so. Nothing critical is missing for an agent to call it correctly.

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 the schema already documents country, service and renews_on fully. The description only implies that renews_on is required for use and adds no syntax or format detail beyond the schema, so it sits at the baseline.

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: it generates a calendar (.ics) reminder for the last safe day to cancel a subscription. It is clearly distinguishable from the sibling cancelmysub_get_cancel_steps, which returns steps rather than a calendar artifact.

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?

Explains the triggering condition – the /v1/cancel endpoint surfaces this as add_to_calendar whenever renews_on is given and the day hasn't passed – which tells the agent when this is relevant. It stops short of explicitly naming sibling tools or stating when not to use it.

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