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

Annotations cover the world/interactivity profile (openWorldHint=true, readOnlyHint=false), and the description adds genuinely useful context beyond them: payment is required and handled natively via x402 with no API key, and there is venue fallback between two exchanges. It stops short of stating cost, latency, or fallback ordering, but the payment requirement is the key missing-from-annotations fact and it is disclosed.

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?

Three tight sentences with the capability front-loaded, followed by the payment/no-key note and an example. Every element earns its place, though the example largely restates the schema description rather than contributing new 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?

With no output schema, the description should carry return-value expectations, and it only hints at them via 'normalized' and 'market context' without saying what a response contains (both venues? merged? per-venue fields?). Payment is covered and the input example is present, so the gap is moderate rather than severe for a one-parameter tool.

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%, but the single 'input' parameter is a freeform object with additionalProperties and no defined subfields, so the example {symbol, providers} is the only real signal about parameter shape — and it is duplicated verbatim from the schema description, adding no meaning beyond it. On the coverage rule this sits at the baseline 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?

Specific verb+resource: 'Fetch normalized live perpetual-futures funding rates' with named venues (Binance + Bybit) and stated behavior (venue fallback, market context). It clearly distinguishes itself from the generic payment plumbing siblings, though it doesn't explicitly contrast with execute_paid_product, which an agent may still wonder about.

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?

'Native x402 payment, no API key' plus a concrete invocation example implies when the tool fits, but there is no explicit when-to-use/when-not guidance and no alternative named. An agent gets an implied use case (live perp funding rates for these venues) but must infer the boundary against the sibling payment-execution tools.

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