fastmail_list_masked_emails

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

No annotations are present, so the description must disclose behavior. It states only that all masked email addresses are listed, without addressing read-only guarantees, authentication needs, pagination, or response format. The parenthetical clarifies the resource but not the tool's behavioral characteristics.

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?

The description is a single, front-loaded sentence with a useful parenthetical clarifier. Every word serves a purpose, and it avoids redundancy.

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 zero-parameter list tool without an output schema, the description gives the core purpose but omits return value structure, pagination, or any operational caveats. It is adequate for selecting the tool but not fully complete for an agent expecting to parse the response.

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?

The input schema has zero parameters with 100% coverage, so there is nothing for the description to add beyond the schema. Baseline for zero-parameter tools is 4, and the description does not need to explain parameters.

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 uses a specific verb ('List') and resource ('masked email addresses') with a clarifying parenthetical defining them as privacy-focused aliases. It is clearly distinct from listing regular emails, though it does not explicitly reference sibling tools to differentiate.

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 description offers no guidance on when to use this tool versus the sibling tools such as fastmail_create_masked_email or fastmail_list_emails. It only restates the tool's function without any exclusions or alternative conditions.

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