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

Annotations already declare readOnlyHint/destructiveHint/openWorldHint=false, so safety is largely covered; the description still adds value by restating non-mutation explicitly and by disclosing the provider value ('ics' in this phase) and the event-count semantics for the current phase. It does not mention auth requirements or what a disabled feed looks like, which would be the next useful detail.

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 sentences, front-loaded with the purpose and followed by scope and return shape; no wasted clauses. Minor redundancy between "Read-only and non-mutating" and the already-declared readOnlyHint annotation, but it is defensible emphasis.

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 parameters and no output schema, the description carries the return contract itself by listing { feed_enabled, feed_url, provider, event_count }. An agent has everything needed to decide to call it and to interpret the result.

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?

There are zero parameters and the schema is trivially empty at 100% coverage, so the baseline is 4. The description correctly implies the caller identity scopes the result ('the caller's calendar feed'), which is the only semantic an agent needs here.

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?

"Report the state of the caller's calendar feed" is a specific verb + resource, and the description enumerates the exact facts returned (subscribe URL presence, URL value, provider, event count). It does not name or differentiate from the close sibling get_calendar_feed_url, so it stops short of fully disambiguating, but the purpose itself is unambiguous.

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 parenthetical "does NOT create a feed" gives an explicit when-not signal that steers an agent away from using this as a mutation/creation call. There is no positive routing to an alternative (e.g. a rotate or create tool) for the case where the caller actually wants a feed, so guidance is clear but incomplete.

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