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

Annotations already declare a safe read-only, idempotent operation, yet the description adds substantial non-obvious behavior: the newest quarter is still filling in, positions are aggregated per filer CIK (with the BlackRock 42-line example), one book per filer (13F-HR or HR/A restatement, add-ons excluded), USD normalization, and the total_value_usd double-count caveat flagged by coverage_caveat.

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?

Long but densely packed — the core 'who owns a stock' purpose is front-loaded, followed by examples, input modes, and caveats. Nearly every sentence carries operational weight, though the coverage/aggregation paragraph is heavy enough that some trimming is conceivable.

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 multi-parameter, nested-object tool with no output schema, the description covers scope, coverage window, aggregation policy, caveats, and 13F limitations (no shorts, cash, bonds, non-US). Nothing an agent needs to invoke it correctly appears 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%, so baseline is 3, but the description adds real meaning: ticker is resolved via CUSIP internally, cusip should be used when the ticker is unmapped, period defaults to the most recent loaded quarter, and issuer is an alias shape shared with financial_search/search. This goes beyond the structured fields.

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 — institutional holders of a security from SEC Form 13F — plus the ranking (position value) and the delta dimension (quarter-over-quarter share changes). It is clearly the inverse of the sibling holdings_by_manager, so an agent can select it without ambiguity.

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 concrete triggering questions ('who are the largest holders of NVDA', 'which funds added or trimmed') and states the input modes (ticker or CUSIP). It implicitly routes against holdings_by_manager via the 'who owns a stock' framing, but never explicitly names when not to use it or points to the sibling by name.

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