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

Goes well beyond the readOnly/openWorld/idempotent annotations: it discloses the $0.005 USDC price on Base, the x402 flow, that an unpaid call returns a PaymentRequired object rather than data, and the exact retry mechanism via params._meta["x402/payment"]. That is precisely the kind of non-obvious behavior an agent would otherwise stumble on.

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?

Front-loaded with the returned fields, then chains, then pricing/payment mechanics — a sensible order. Mild redundancy in re-listing the chain enum and the HTTP route, but the density is justified for a paid tool.

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 present, the description carries the full burden and does so by enumerating every returned field including raw and decimal amounts. Payment, retry, supported chains, and the HTTP equivalent are all covered, leaving nothing an agent needs to call 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 50% (only tx is described), and the description compensates by enumerating the eight valid chains and characterizing tx as a transaction hash for an on-chain tx. It also documents the payment parameter _meta["x402/payment"], which appears nowhere in the schema — genuinely added semantics.

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 resource and the exact payload returned: success, block, UTC time, confirmations, sender, and every ERC-20/ERC-721 transfer decoded from the receipt. The framing 'Payment proof for any EVM tx' plus the chain list cleanly separates it from siblings like address_transfers (address-scoped) and tx_decode (decoding-only).

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?

The phrase 'Payment proof for any EVM tx' implies the use case, but the description never explicitly contrasts with address_transfers or tx_decode, nor states when-not to use it. The payment retry procedure is spelled out, but tool selection guidance is left to inference.

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