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

Annotations only tell the agent this is a non-destructive write. The description adds substantial context beyond that: no position fields are stored (no quantity/cost/value), the option contract is verified against live options data before persisting, and the exact downstream representation in GetMyPortfolio is described.

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?

Three short paragraphs, front-loaded with the core action and the 'not held' distinction. Every paragraph carries weight, though the third paragraph on already-held instruments is a minor edge-case elaboration that could be tightened.

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?

There is no output schema, yet the description fully covers what an agent needs: what is stored, what is verified, symbol formats for both stocks and options, and how the result appears in GetMyPortfolio. Nothing material for correct invocation 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 already 100%, so the baseline is 3, but the description adds real meaning by describing the relationship between parameters - pass BOTH the underlying ticker and the OCC symbol to watch an option, omit optionContract for the stock - which clarifies the ticker/optionContract combination beyond the individual 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+resource: 'Put a stock or an option contract on one of the USER's portfolio watchlists, without recording any position.' It immediately differentiates itself from position-recording siblings like AddPortfolioLot and clarifies the resulting state in GetMyPortfolio's 'Watching (not held)' section.

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?

Clearly frames the when: this is for watching, not holding, and explicitly notes that watching something already held is allowed and that selling out keeps it on the list. It references AddPortfolioLot for input format but does not explicitly name it as the alternative for recording positions, so the routing is strong but not fully spelled out.

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