list_rules

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

With no annotations provided, the description carries the full burden. It discloses the read-only nature, that rule names are not guaranteed unique (Mail allows duplicates), and that rules have no stable id via AppleScript. It also provides a concrete return example. It does not cover potential errors or edge cases, but for a simple read-only list this is a solid disclosure.

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 clear and front-loaded with the core purpose. The duplicate-name caveat and read-only note are useful. The example clarifies the return shape without excessive verbosity. It could be slightly tighter by merging the 'Returns' line into the example, but overall it is efficient.

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, read-only list tool, the description covers the essential domain information: what it returns, the uniqueness caveat, and the mutation separation. It does not address error conditions or the absence of an id field, but these are minor for this simple operation. The presence of an output schema (via example) further reduces the burden. Overall it is complete enough for an agent to call correctly.

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 tool has zero parameters, so the schema is trivially complete. Per rubric, 0 params gives a baseline of 4. The description adds no parameter-specific meaning because none exist, and none is needed.

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?

Begins with 'List all Mail.app rules' — a specific verb and resource. The read-only qualifier immediately distinguishes it from mutation siblings like create_rule/delete_rule/update_rule. The description fully identifies the tool's function without ambiguity.

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?

States 'This tool is read-only; mutation (enable/disable, create, delete) is tracked as a separate enhancement,' which clearly signals when not to use this tool. However, it does not explicitly name the alternative sibling tools (create_rule, update_rule, etc.), relying on the agent to infer from the sibling list. Still, the context is clear enough for correct selection.

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