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

Annotations already declare readOnlyHint=true, so the bar is lowered, but the description adds real value by stating 'Read-only despite being a POST' — resolving the exact confusion a POST endpoint would create. It also cites the underlying HTTP route. It does not, however, discuss pagination behavior or filter semantics.

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?

Two tight sentences: scope first, then the read-only clarification and endpoint. Every clause earns its place with no filler.

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, so return values need not be explained, and pagination/filters live in the schema. Combined with the read-only POST warning and endpoint, the definition is nearly complete; only filter behavior on nested objects is left unaddressed.

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 coverage is 100%, so all four parameters (list_id, page, filters, results_size) are already documented in the schema; baseline is 3. The description occasionally hints at content ('blocked IPs, emails or device ids') but adds no new parameter syntax or format detail.

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?

Names a specific verb (search) and resource (entries of one list), and clarifies what the list contains (blocked IPs, emails, device ids). This disambiguates it from siblings like castle_count_list_items, castle_get_list_item, and castle_search_lists without opening their schemas.

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 phrase 'Search the entries of one list' implies the usage context but gives no explicit when-to-use guidance or alternatives (e.g., count vs. get item vs. search lists). An agent must infer the routing from sibling names.

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