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

With annotations already declaring readOnly, idempotent, and non-destructive, the bar is lower. The description adds value by disclosing the return payload (ticker, shares, market value, report period) and scoping to the 'latest' report, which is genuinely useful given there is no output schema.

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-loaded with the core question and scoping; the trailing example call is somewhat redundant with the schema's examples list but confirms required fields compactly. Minimal waste overall.

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 read-only, no-output-schema tool, the description covers purpose, required identifier format, and returned fields, which is enough to call it correctly. Only the sibling differentiation and explicit usage routing are absent.

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%, so the schema already documents all three parameters. The description's CIK example and 'not a fund name' note largely duplicate the filer_cik schema text, adding no new format or syntactic detail. 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 and resource — 'every long position an institutional filer reported in its latest SEC Form 13F' — with a concrete example (Berkshire CIK). It clearly conveys the 13F-holdings concept, though it never names its closest sibling fd_institutional_holders, so the agent must infer the distinction.

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?

Usage is only implied. The constraint 'requires a CIK, not a fund name' is a useful precondition, but there is no explicit when-to-use/when-not guidance and no routing to alternatives such as fd_filings or fd_institutional_holders despite them appearing in the sibling list.

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