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

Annotations already declare readOnlyHint, idempotentHint and non-destructive, so the safety profile is covered. The description adds genuinely new behavior: an account prerequisite and a Premium gating rule for named custom lists. It does not mention pagination or size limits, but nothing is contradicted.

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 sentences, each earning its place: identity of the result, the selection/default rule plus constraints, and follow-up routing. The key scoping information is front-loaded.

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?

With no output schema, the description still conveys the return shape (symbols plus their pinned sector). For a single optional-parameter read tool with full annotation coverage, an agent has everything needed to decide and call.

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 documents `list` with its default. The description adds meaning beyond the schema by tying custom list names to the Premium tier and clarifying that the unnamed case resolves to "Favorites".

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: the signed-in user's saved symbols, each with its pinned sector. It names the default list and explicitly routes figure lookups to zensei_stock_detail and zensei_sector_detail, so an agent can distinguish it from the sibling detail/scan tools without opening schemas.

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?

Explicit conditions are given: reads "Favorites" unless `list` names another list, requires a Zensei account, and custom lists are Premium-only. It also names the follow-up tools to use for figures, which is concrete alternative routing.

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