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

The annotations already declare this as a read-only, non-destructive, closed-world operation, so the safety profile is covered. The description adds real behavioral facts beyond that: fixed 100-per-page pagination and a paid-plan requirement. It says nothing about ordering or what an empty/unknown list returns, which is a modest gap for a read tool.

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 short sentences with zero filler, front-loading what is returned and at what page size before naming the alternative and the plan constraint. Every clause carries information the agent uses.

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 two-parameter read tool with full schema coverage and annotations, the description covers purpose, pagination size, plan gating, and the sibling alternative. It leaves open how to target the blacklist and how to enumerate valid list ids from the agent's side, though the schema points at listWatchlists.

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 both parameters are already documented, and the baseline would be 3. The description adds meaning on top: it quantifies the page size (100 per page) and implies listId can address either a watchlist or the blacklist. The blacklist encoding remains unstated.

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 the specific verb and resource: gets the domains of one watchlist or the blacklist, returned 100 per page. It also distinguishes itself from searchStores, which returns store data rather than domains. The only ambiguity is how the 'blacklist' is selected, since the tool requires a listId and never says which value selects it.

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?

Explicitly routes the agent to searchStores with tab "watchlist:{id}" when store data (rather than domains) is wanted, which is a genuine when-to-use-this-instead signal. It also states a prerequisite, 'Paid plans only.' It does not mention listWatchlists as the way to obtain listId, though the schema does.

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