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

Annotations only say it is a non-destructive write; the description adds substantial behavior the annotations cannot convey: authorization requirement (house owner only), a quota (up to 5 feeds), pre-save validation of the feed, and asynchronous propagation ('events appear after the feed's next refresh, which can take a few hours').

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?

Four compact sentences, front-loaded with the action and outcome, then constraints and timing. The typed-by-user rule is partially duplicated from the feedUrl schema description, which is minor redundancy rather than bloat.

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?

An output schema exists, so return values need not be explained. The description covers the remaining agent-relevant unknowns: permission, quota, validation, and the delayed-sync caveat.

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 coverage is 100%, so both parameters are already documented, including length limits and the typed-by-user trust rule. The description restates that rule but adds no syntax or format detail 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 (subscribe) plus resource (household to an external .ics calendar feed) and describes the outcome (events appear in the household calendar and stay in sync). This clearly distinguishes it from siblings like create_calendar_event (single event) and create_subscription (generic subscription).

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 strong when-to-use constraints: only subscribe to a feed URL the user typed in this conversation, owner-only, max 5 feeds per house. It does not explicitly contrast with the sibling create_subscription, so the agent must infer which tool owns a non-ICS subscription.

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