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

Annotations already declare readOnlyHint=true and idempotentHint=true, and the description adds rich behavioral guarantees: it NEVER substitutes the latest period, NEVER returns 0 for missing data, NEVER lets a 9-month YTD answer a quarterly question, and NEVER converts currency. It also describes the full response contents (us-gaap concept, accession number, filing link, restatement trail) and the meaning of each non-answer status, going far 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?

The description is long and uses ALL CAPS and em-dashes heavily, which slightly hurts readability. However, it is front-loaded with purpose and examples, and every sentence carries substantial information about behavior, statuses, and source. Given the tool's complexity (6 params, nested objects, no output schema), the length is mostly justified, though a structured layout would improve conciseness.

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 tool with no output schema, this description is remarkably complete: it explains the period model (filer's own fiscal year), the attribute set, each non-answer status in detail, the data source (SEC EDGAR XBRL companyconcept), and even the alternative REST endpoint. An agent can determine when and how to call it correctly without additional context.

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 baseline is 3. The description adds illustrative examples (Apple revenue, Walmart net income) and clarifies the annual vs quarterly distinction, but the schema already documents these semantics in detail (e.g., 'quarterly' = ONE discrete quarter). The description adds marginal value beyond the schema, so 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 opens with a specific verb and resource: 'TYPED, DETERMINISTIC financial facts for a US public company for an EXPLICITLY NAMED reporting period', and gives concrete examples. It explicitly contrasts with entity_profile / get_company_financials, stating those return 'the most recent figures' and may hand back the wrong fiscal year, which clearly distinguishes it from siblings.

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 states 'PREFER OVER entity_profile / get_company_financials whenever the period matters' and explains why those tools fail (fiscal-year substitution, quarter vs YTD confusion). It also details the named statuses (unavailable, unsupported, ambiguous, etc.) which further clarifies when this tool is appropriate and what to expect otherwise.

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