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

Beyond the annotations, the description discloses auth requirements, that the call is free, the partial-update rule ('Kinds not named keep their setting'), and the return value ('Returns the preferences after the change'). It also equates a full unsubscribe with the unsubscribe link, which tempers the destructiveHint. It does not state whether the change is logged, confirmed, or how to verify afterward.

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?

A single front-loaded sentence chain that defines the main switch, then the granular switch, then the partial-update rule, then cost, return, and auth. No clause is filler and nothing important is buried.

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, fully described schema with no output schema, the description covers action, scope, partial-update behavior, return value, cost, and auth. The only meaningful omission is any pointer to `get_email_preferences` as the non-mutating alternative.

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 the baseline is 3, but the description adds meaning the schema does not: it explains that `subscribed` is an all-or-nothing global switch and that unspecified `kinds` entries are left untouched, which is the key merge semantic for a nested object.

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 opens with a specific verb and resource ('Turns automated emails on or off') and immediately defines the semantics of both `subscribed` values and the `kinds` map, so an agent knows exactly what the tool mutates. It does not explicitly name the read counterpart `get_email_preferences`, which keeps it from a 5.

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?

Clear conditions are given for each mode: `subscribed: false` for a full unsubscribe, `subscribed: true` to resubscribe, `kinds` for individual switches, plus the key rule that unnamed kinds keep their setting. Prerequisites ('Needs an API key or a connected account') and cost ('Free') are stated. It never explicitly says to use this rather than `get_email_preferences` when only reading.

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