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

Beyond the annotations (idempotentHint, readOnlyHint false), the description discloses that duplicates are skipped, that the watchlist has a plan-dependent cap that can cause partial acceptance, and that the agent should report confirmed tickers rather than assuming all were added. This adds meaningful behavioral transparency that annotations alone do not provide.

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?

The description is four sentences, each serving a distinct purpose: purpose, idempotency, usage condition, and limit/reporting. It is front-loaded with the primary action and contains no redundant or filler content.

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 an add-to-watchlist tool with an output schema present, the description covers when to call, duplicate handling, plan limits, partial acceptance, and reporting requirements. The sibling tools and annotations complement this, making the description complete for safe and correct invocation.

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?

The input schema already documents the 'tickers' parameter with an example array (['AAPL', 'MSFT', 'BTCUSD']), achieving 100% schema description coverage. The description does not add additional parameter-level detail beyond referencing tickers in context, so the baseline 3 for high schema coverage is appropriate.

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?

The description opens with 'Add tickers to the user's saved watchlist', a specific verb+resource statement that clearly distinguishes the tool from the sibling get_watchlist and remove_from_watchlist. The duplicate-skipping behavior further clarifies the operation's scope.

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 gives explicit when-to-use guidance: 'Only call this when the user explicitly asks to track, save, or watch a ticker; do not add tickers just because they came up in conversation.' It also points to get_account for the plan's watchlist_limit, providing a cross-reference for capacity constraints.

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