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

Annotations already declare readOnlyHint=true, but the description adds genuinely useful context by preempting the HTTP-method confusion: 'Read-only despite being a POST.' It also exposes the underlying REST route, which helps an agent map intent to the API. It stops short of describing pagination behavior or result limits beyond what the schema carries.

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?

One tightly packed sentence plus a short clarifier and the route. Nothing is redundant and the resource scope is front-loaded before the method caveat.

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 read-only filtered-list tool with a fully documented schema and no output schema, the definition covers purpose, scope and the POST/read-only nuance. The only minor gap is pagination/return-shape guidance, which the schema's page and results_size parameters largely imply.

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 page, results_size, filters and list_id are already documented in the schema with ranges and semantics. The description adds only the resource framing ('entries of one list') and no extra syntax or format detail, so the baseline of 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?

States a specific verb (search) and resource (entries of one list), and clarifies the resource scope by enumerating what a list holds (blocked IPs, emails, device ids). This cleanly distinguishes it from the sibling castle_search_lists, which searches the lists themselves rather than their entries.

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 implies usage (query the items inside a given list) and the required list_id makes the scope explicit, but it never states when to prefer this over castle_get_list_item or castle_count_list_items, nor any prerequisites. Usage is inferable rather than spelled out.

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