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

Annotations already declare readOnlyHint=false, idempotentHint=true, destructiveHint=false and openWorldHint=false. The description adds genuine context beyond them: server-side storage that follows the API key, a 50-symbol limit, and that mixed asset classes are permitted. What happens when the cap is exceeded (error vs. truncation) is left unstated.

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 tight sentences; the core action leads, followed by the constraints and format. No filler, every clause carries operational information (storage model, limit, syntax, examples, mixing rule).

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 tool with no output schema and annotations covering the safety profile, the description covers action, persistence, limit and input format. The only meaningful omission is behavior at the 50-symbol ceiling, which an agent may need to set expectations.

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 schema already says 'comma-separated EXCHANGE:SYMBOL list', so baseline is 3. The description rises above it by supplying concrete format examples across exchanges and explicitly noting that crypto, stocks, futures and FX can be mixed in one list, which removes real ambiguity in constructing the value.

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 (user's personal watchlist), and the scope is unambiguous against siblings like watchlist_remove and my_watchlist. An agent can distinguish this from the read/remove siblings 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 clear operating context: server-side persistence tied to the API key across MCP clients, and a hard cap of 50 symbols. It does not explicitly name when to prefer it over siblings (e.g. my_watchlist for reading, watchlist_remove for deletion), but the add semantics make the alternative obvious.

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