Current funding rate, next funding time, mark/index price and open interest for a perpetual from Bybit and OKX, with annualised funding. 0.002 USDC per call via x402.
| Name | Required | Description | Default |
|---|---|---|---|
| symbol | Yes | Base asset, e.g. BTC, ETH, SOL | |
| paymentProof | No | Payment proof: USDC tx hash on Polygon or Base (0x...) or Solana tx signature. Omit on the first call to receive the 402 payment instructions, pay, then call again with the proof. |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description does carry useful behavioral weight: it discloses the per-call cost and the x402 payment model, which is a critical trait an agent must know before invoking. However, it omits other important behavior for a paid call — what happens on an unpaid call (the 402 handshake is only in the schema), failure/insufficient-payment behavior, and rate limits.
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?
Two dense sentences with zero filler: the data payload and venues come first, the pricing model second. Nothing would be lost if trimmed further, and nothing extraneous is present.
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?
There is no output schema, so the description appropriately enumerates the returned fields (rate, next funding time, mark/index, open interest, annualised funding). Combined with the fully-documented params, an agent has nearly everything needed; the only gap is the unpaid-first-call behavior, which lives in the schema rather than the description.
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 both parameters (symbol and paymentProof) are already fully documented in the schema, including the two-step 402 payment flow. The description adds no parameter-level detail beyond that, so the baseline 3 applies.
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 names the exact data points returned (funding rate, next funding time, mark/index price, open interest) and the two venues (Bybit, OKX), which is far more specific than the name alone. It does not explicitly contrast itself with sibling tools, but no sibling covers perpetual funding, so the distinction is implicit rather than stated.
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?
It says what the tool returns and that it is paid (0.002 USDC via x402), but gives no guidance on when to call it versus alternatives or which symbols are supported beyond the schema's BTC/ETH/SOL examples. The caller must infer the use case from the data field list.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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