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

Annotations already establish this is a non-destructive but non-idempotent, open-world write, so the safety bar is partly met. The description adds real value by disclosing the accepted values per field and by naming the `say` field as the read-ready summary of the result (useful since there is no output schema), but it says nothing about whether omitted fields are left unchanged, defaults, or authorization.

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 purpose sentence followed by a dense but tight per-field value list; no filler. Slightly compressed formatting ('all_optional_off.' attached to the messages clause) costs a little readability.

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 5-param mutation with no output schema and no schema descriptions, the description covers most valuative semantics and the return summary, but leaves `applicants` undefined and does not state the merge/partial-update behavior or defaults for an all-optional call.

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?

With 0% schema coverage and 0 enums, the description carries the entire burden and mostly succeeds: it enumerates the allowed values for alerts, autopilot_mail, messages, and all_optional_off. It omits the `applicants` parameter entirely, leaving one of five params undocumented anywhere.

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?

Clear specific verb+resource ('Change which emails the person gets') that an agent can act on immediately. It does not explicitly distinguish itself from the read-side sibling get_email_preferences or from update_preferences, so sibling differentiation is left to the agent.

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?

No when-to-use guidance, no prerequisites, and no routing to alternatives such as set_preferences_from_text or update_preferences, which are adjacent in the sibling list. Usage is only implied by the name and first sentence.

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