payment_infoFree. Returns the x402 payment requirements (price, USDC/USDT contract, pay-to wallet, network) for a given tool so an agent can construct an x402 payment.
| Name | Required | Description | Default |
|---|---|---|---|
| tool | Yes |
Changes observed during successful MCP inspections.
Input schema / properties / tool / enumPrevious value: -[
- "extract_clean",
- "market_spread",
- "gas_fees",
- "token_price",
- "wallet_balance"
-]New value: +[
+ "extract_clean",
+ "market_spread",
+ "gas_fees",
+ "token_price",
+ "wallet_balance",
+ "web_search",
+ "email_validate",
+ "dns_whois",
+ "pdf_text",
+ "seo_check"
+]Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With readOnlyHint already covering safety, the description adds the genuinely useful behavioral fact that the call is 'Free' (no payment required to discover payment requirements), plus the composition of the payload it returns. It does not cover caching/rate behavior or whether requirements can change over time.
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 tight sentences with the cost fact front-loaded ('Free.') and the return contents immediately after. No filler and nothing buried.
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 correctly spells out the returned fields, which is the right compensation. For a one-parameter read tool this is close to sufficient; only a note on how the agent should use the returned values would make it airtight.
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 0%, so the description must carry the load; it partially does by clarifying the single parameter identifies the target tool. It adds nothing about the enum values or what happens for an unrecognized tool, leaving the schema enum to do the rest.
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 and resource (returns the x402 payment requirements) and enumerates exactly what comes back: price, USDC/USDT contract, pay-to wallet, network. The scoping phrase 'for a given tool' separates it cleanly from the ten sibling tools that actually perform those operations.
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?
States the purpose of the call ('so an agent can construct an x402 payment'), which implies the trigger situation — call this before invoking a paid sibling tool. It does not name which siblings are paid or state an explicit when-not condition, so it falls short of full routing guidance.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.