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

Annotations only declare readOnlyHint=false and destructiveHint=false, so the description usefully adds the account-bound API key requirement and the invariant that keyword tracking depends on watchlist membership. It does not disclose idempotency (re-adding an existing app) or the response shape, but for a non-destructive additive mutation this covers the main operational concerns.

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 sentences, front-loaded with the primary action and then the conditional keyword behavior, then the auth prerequisite. No filler or redundancy.

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, the description carries the burden of explaining behavior, and it covers purpose, prerequisites, and the key/param interaction adequately. Minor gaps remain around duplicate adds and success/failure behavior, which would be needed for a fully complete picture.

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 the baseline is 3, and the description earns above that by explaining the conditional relationship between keyword_id and the watchlist and by noting the storefront matching constraint on country_code. It adds cross-parameter meaning rather than merely restating field docs.

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 ('Add') and resource ('an app to your watchlist') and extends the scope conditionally with keyword_id. It is clearly distinguishable from the read-only siblings like get_keyword_watchlist and get_tracked_apps, which only retrieve watchlist state rather than mutate 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?

Gives a clear precondition ('Needs an API key bound to an account') and a usage rule ('A keyword is tracked only for an app on your watchlist'), which tells the agent the order of operations. It does not explicitly say when to prefer this over other watchlist/keyword tools or when not to call it, so it stops short of full alternative routing.

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