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

With no annotations, the description carries the full burden and does well: it discloses partial-update semantics, a read-only calling mode, and account-level scope. It omits permission/ownership requirements and whether toggling re-scans has cost or scheduling side effects, which keeps it below a 5.

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?

Three short sentences, each carrying distinct information: what is toggled, how to do partial vs. full reads, and the account scope. Nothing is repeated and the core action is front-loaded.

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?

No output schema exists, and the description at least indicates that a no-argument call returns the current settings, which covers the read case. The return shape after a write is left implicit, a minor gap for a two-boolean settings tool.

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 both booleans including the 'leave out to keep current setting' behavior. The description restates the same omission semantics rather than adding new meaning, 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?

The description names a specific verb pair (turn on/off) and a specific resource (the signed-in person's monthly re-scans and result emails). The closing sentence 'The settings belong to the account, not to one site' explicitly separates it from the site-scoped siblings like scan_page or request_site_scan.

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?

It states the partial-update rule ('Leave a field out to keep it as it is') and the read path ('call with no fields to read the current settings'), which tells an agent exactly how to invoke it in both modes. It does not name alternatives or exclusions, but no sibling tool competes for this operation.

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