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

Annotations cover the safety profile (readOnly, idempotent, non-destructive), but with no output schema the description carries the return-value burden and does so richly: it enumerates all five statuses, explains the 'partial' itemised claimed-vs-filed behaviour, states the coverage window is always reported, and declares Rule-2 (absence reported as absence, no estimates). That is behavioural context well beyond the annotations.

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 action, then the status vocabulary, then the coverage/Rule-2 guarantees. It is dense but every clause (statuses, coverage window, no-estimates rule) earns its place. Slightly heavy as one block of prose, keeping it from a 5.

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 9 params at full schema coverage, no output schema, and closed-world annotations (openWorldHint=false), the description supplies exactly the missing piece: the return-status taxonomy and the coverage-window guarantee. Nothing an agent needs to invoke or interpret it correctly is 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 description coverage is 100%, so the schema already documents every parameter, including the ±3 filing-day date tolerance and the ±5%/±$1 amount tolerance. The description only restates the claim fields (ticker/issuer, person, amount, timeframe) without adding syntax or matching semantics beyond the schema, so 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+resource: 'Check a claim about an insider open-market buy ... against the filed record.' The parenthetical enumerates the claim dimensions (ticker/issuer, person, amount, timeframe), and the opening clause immediately distinguishes this verification tool from the signal/aggregation siblings (insider_signals_*, insider_cluster_buys).

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?

Explicitly scopes usage by stating only open-market buys are covered and that sales/options/grants return out_of_scope, which tells the agent when this tool is the wrong choice. It stops short of naming a specific alternative sibling (e.g. insider_filing_lookup) for the out-of-scope cases, so it is clear context without full alternative routing.

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