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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is known. The description adds genuinely new behavior: the auth requirement, the full failure surface (400 invalid_list, 400 invalid_entry, 404 list_entry_not_found, inbox_not_found), and what inbox_id omission means for scope.

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?

Four tightly packed sentences with no filler: purpose first, then access/scope, then inputs, then return shape and failure modes. Every clause carries information an agent needs.

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?

With no output schema present, the description supplies the returned object's fields, plus auth requirements and the full error enumeration. Nothing needed to invoke this read correctly is missing.

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% and two parameters carry enums, so the schema already documents direction, type, entry, and inbox_id semantics. The description restates those values and the account-wide scoping rule rather than adding syntax or matching behavior beyond what the schema contains, so the baseline 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 precise verb and resource ('get one ... entry') scoped to allow/block lists, and the title reinforces the singular-entry scope. It is immediately distinguishable from cooper_list_list_entries (enumerate) and cooper_create_list_entry/cooper_delete_list_entry (mutate).

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?

'Use this when you need one address or domain on an allow or block list' gives a clear triggering condition, and the singular phrasing implicitly contrasts with the list counterpart. It never explicitly names the alternatives or states when not to use it, so it stops short of the top band.

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