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

Annotations already declare it a read-only, idempotent, open-world operation, so the safety profile is covered; the description adds genuinely non-redundant behavior: paid ($0.02 USDC on Base via x402), live-fetched from data.sec.gov, wallet never custodied by the server, and the two-step challenge/retry handshake.

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-loads the paid tag and the core resource description, then covers the payment flow in one compact sentence. Slightly redundant in restating the price and 'your own wallet pays' twice, but no sentence is wasted.

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 4-param, 0-required tool with nested payment object and no output schema, the description discloses what is returned (concept value, period end, form, filed date), the data source, and the full payment handshake. Only the sibling/alternative routing is left implicit.

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% and every field (cik, ticker, concepts, payment_header) is already documented in the schema, so the baseline is 3. The description echoes the payment_header mechanics but adds no syntax or format detail beyond the schema.

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 combo: fetch key XBRL facts (Assets, Revenues, NetIncomeLoss, EPS) for a US-listed company by ticker or CIK, with the source (data.sec.gov). It is clearly distinct from filings/fulltext siblings, though it never names the paid-vs-preview sibling (edgar_company_facts_preview) that an agent would most need to disambiguate.

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 an explicit operational workflow: call with no payment_header first to receive the x402 challenge, then re-call with the same business arguments plus the signed header. It does not, however, advise when to prefer this over the preview or the bundle/filings alternatives.

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