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

With zero annotations, the description carries the full burden and does disclose the traits that matter most for a paid endpoint: it is paid, the exact price and settlement chain ($0.05 USDC on Base), that no account or API key is required, and the literal endpoint URL. It stops short of describing the response payload, ordering, or what happens on payment failure.

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?

Extremely compact and front-loaded: the 'Paid.' prefix immediately sets the commercial framing, then resource, then price, then auth. The telegraphic fragments cost some readability but every clause carries information.

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 one-optional-parameter tool with no annotations and no output schema, the description covers purpose, cost, and auth adequately. It leaves the return shape and the meaning of the 'ECF' identifier unexplained, which an agent would need to confirm before paying per call.

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% — the single 'limit' parameter is documented in-schema as rows 1-100 with a default of 20. The description adds nothing about it, so the baseline of 3 applies since the schema does all the work.

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 resource: open-market insider BUYS from SEC Form 4 for ECF, with the filer categories (officers, directors, 10% owners) spelled out. It is clearly distinguishable from buy_coin_* or buy_pm_* siblings, though it never explicitly says ECF is a ticker or contrasts itself with the generic buy_insider tool.

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?

Usage context is implied (this is the paid ECF-specific insider-buys endpoint), and it does state the commercial prerequisites: $0.05 USDC on Base, no account or API key needed. However, there is no explicit when-to-use versus buy_insider (the unfiltered sibling) or guidance on when a caller should not pay for this data.

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