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

Annotations already declare non-destructive, idempotent, non-open-world. The description adds real value beyond them: the free-tier cap, that listed stocks are left unchanged, the downstream effect on email alerts and the weekly briefing, and that the response reports exactly what changed. Missing only failure behavior (e.g. what happens when the cap is exceeded).

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?

Four short sentences, front-loaded with the action and limits, then the data-source dependency and response behavior. Each sentence adds information; only the repeated 'free accounts up to 10' phrasing costs it a point.

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 scope, idempotency, side effects on alerts, required input format, and return behavior. Nothing material is missing for an agent to call it correctly.

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% and the single symbol parameter is fully documented in the schema including format examples. The description's 'symbols as returned by resolve_stock' restates the schema rather than adding syntax or format detail, so the baseline 3 applies.

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 (watchlist) with scope limits (up to 10 on free, unlimited Pro), which cleanly separates it from remove_from_watchlist and get_watchlist. An agent can identify what it does without opening the 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?

It names the prerequisite data source ('Takes symbols as returned by resolve_stock') and gives the triggering condition ('when the user asks for this change to their own account'). No explicit when-not guidance, but the context is clear enough to route correctly against siblings.

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