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

Annotations already declare destructiveHint=true, and the description adds the meaningful detail that the list can be allow or deny and references the underlying POST /v1/lists endpoint. It does not explain what allow vs deny changes downstream, nor that creating a list is purely additive despite the destructive hint — a mildly confusing signal left unaddressed.

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, front-loaded with the action and the key semantic field. The trailing 'Castle: POST /v1/lists' is low-value endpoint trivia but costs little.

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 five-parameter creation tool with full schema coverage and no output schema, the description covers the essentials. It does not state what is returned (e.g., the new list ID) or whether the primary_field is immutable after creation, both of which an agent might need.

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 all five parameters including name, color, and secondary_field are already documented. The description's explanation of primary_field ('the event field its entries match on') duplicates the schema text rather than adding syntax, allowed values, or examples.

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?

States a specific verb and resource ('Create a new allow or deny list') and clarifies that primary_field is the matching event field, which goes beyond the title. It never names or differentiates itself from siblings such as castle_create_list_item or castle_update_list, so the distinction rests on the tool name alone.

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?

There is no when-to-use guidance, no prerequisites, and no mention of alternatives like castle_update_list (for existing lists) or castle_create_list_item (for entries). The agent must infer from the name that this is the creation path.

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