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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds valuable behavioral context beyond annotations: 13F filings lag the quarter by up to 45 days, show long positions only, and cost $0.02 per call with a payment-required error for unpaid calls. This is exactly the kind of real-world caveat an agent needs.

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?

Four sentences, each earning its place: what the tool returns, the data caveat, the sibling alternative, and the cost/error condition. The core purpose is front-loaded, and the guidance is compact.

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 read-only tool with a full output schema, the description covers the data returned, the timing caveat, the alternative tool, the prerequisite lookup, and the cost/error behavior. Nothing an agent needs to decide whether to call it 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 description coverage is 100%, so the schema already documents the cik parameter fully, including an example (320193 for Apple) and a pointer to lookup_company. The description doesn't add parameter-level detail beyond that, but it doesn't need to. Baseline 3 is appropriate.

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?

The description states a specific verb ('snapshot') and resource ('13F institutional ownership for one company'), and enumerates the exact data points returned (number of holders, aggregate shares/value, QoQ change). It also distinguishes itself from company_signal, a sibling that scores institutional positioning alongside other factors, so an agent can tell them apart.

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?

The description explicitly says when to use this tool (for a 13F snapshot) and when not to (use company_signal for institutional positioning scored alongside other factors). It also gives a concrete prerequisite: if you only have a ticker or company name, call lookup_company first. This is clear routing guidance.

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