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

Goes well beyond the readOnlyHint annotation: exact return shape on every path, the absence of a price leg (no price/market value/gain/weight), the empty-list-on-unknown-id behavior, and the API-key auth requirement. This is unusually rich disclosure for a read tool.

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 what it returns and what it lacks; every sentence carries information. The capitalized emphasis ('ONLY', 'THERE IS NO PRICE LEG') is slightly noisy but justified for preventing hallucinated price fields.

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 fully compensates by specifying the return object, its fields, sorting, null semantics, and failure behavior. Nothing an agent needs to interpret the response 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 coverage is 100% and there is a single optional portfolio_id already documented with its default, so the schema carries the parameter meaning. The description only adds that an unknown id yields an empty list, which is behavioral rather than syntactic.

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 ('Stored positions of one saved portfolio') and explicitly distinguishes itself from the sibling get_sector_breakdown for the catalog-wide sector mix. An agent can identify it without inspecting 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?

Names the alternative tool and the condition that selects it (sector mix -> get_sector_breakdown), and warns that an empty list does not prove existence. It does not spell out broader when-to-use/when-not scenarios, but gives clear context.

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