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

Annotations already declare readOnlyHint=true and destructiveHint=false, and the description adds substantially beyond them: ~2700s response caching, auth mechanisms (X-Api-Key or x402 payment proof), HTTP 402 behavior for anonymous calls, $0.003 USDC per-call cost, and a 30/min rate limit. The billing clarification ('This is billing, not a side effect') is exactly the kind of context an agent needs before calling a paid endpoint.

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 first sentence of the description is repeated verbatim in the 'Purpose:' paragraph ('BloFin derivatives data: BloFin open interest and funding, and a bulk scan of BloFin tickers and funding. Paid calls carry BloFin and public-domain (CFTC) data only.' appears twice). This redundant duplication wastes a substantial fraction of the text, even though the auth/cost/rate-limit block is genuinely informative.

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?

An output schema exists, so return values need not be explained here, and the description still summarizes them ('Normalized market microstructure data'). Combined with full parameter coverage, complete annotations, and explicit auth/cost/rate-limit/guideline notes, an agent has everything required to invoke this correctly.

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 both parameters (symbol, __x_payment) are documented in the schema, so the description adds no syntax or format detail for symbol beyond 'default: top 20' which the schema already states. Per the rubric, a high-coverage schema sets the baseline at 3.

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?

Names a specific verb (call/retrieve) and a concrete resource: BloFin open interest, funding, and a bulk scan of BloFin tickers. An agent can distinguish it from siblings like cc.open_interest or cc.funding_rates, though the description never explicitly contrasts with them. The opening line and the 'Purpose:' paragraph are verbatim duplicates, which slightly muddies the otherwise clear statement.

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 real context: 'Use for research / signal context,' and routes the agent to cc.agent_strategy (paper) before any live order, plus a caution not to invent fills from this data alone. It stops short of stating when NOT to use it versus the other derivatives siblings (cc.open_interest, cc.funding_rates, cc.blofin_public), which are the tools most likely to be confused with it.

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