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

Goes well beyond the annotations: it discloses that existing entries are left unchanged (context for idempotentHint), that the watchlist drives email alerts and the weekly briefing (a real side effect), and that the response reports exactly what changed plus buy_rules/buy_rules_note per stock. That is substantive consequence disclosure an agent could not infer from the structured fields.

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?

Front-loads the action and cap, then layers constraints, side effects and return shape in a logical order with no filler. A couple of sentences are slightly tangled (the buy_rules_note clause reads awkwardly), which keeps it off a 5.

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 single-parameter mutation with no output schema, the description covers limits, duplicate handling, downstream effects and return contents, which is nearly everything needed to call it correctly. It omits error/failure behavior (e.g. what happens past the 10-stock free cap) and any auth requirement.

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?

With one parameter at 100% schema coverage, the schema already documents the array, maxItems of 10 and the format. The description's 'takes symbols as returned by resolve_stock' and the 10-stock cap restate what the schema and annotations already say, adding little new meaning.

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 and resource ('Add up to 10 stocks to the watchlist') plus the account scope ('the user's Fair Value Calculator account'), which cleanly separates it from get_watchlist and remove_from_watchlist without opening any schema.

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 usage condition ('when the user asks for this change to their own account') and an implicit boundary against suggestion tools via 'suggest_watchlist_stocks', and notes the free-tier limit of 10. It stops short of naming an explicit alternative or a when-not case, so it is strong but not fully routing-aware.

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