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

Annotations only declare readOnly=false/openWorld=true/idempotent=false/destructive=false; the description adds the material facts those annotations cannot convey — a $0.01 USDC-on-Solana charge, the x402 challenge-and-retry handshake, and an HTTP equivalent endpoint. It does not cover rate limits, caching, or behavior on an invalid/unknown hash, so it stops short of a 5.

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?

Purpose is front-loaded in the first clause, then payment mechanics follow. Dense but every sentence carries operational weight; the nested parenthetical payment retry instruction is slightly run-on but justified by the complexity it encodes.

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 compensates by enumerating the returned fields (function, args, amounts, ENS), and it fully covers the non-obvious cost and payment flow. For a one-parameter paid decoder, an agent has everything needed to call it 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?

The single parameter is fully documented in the schema (0x-prefixed 32-byte transaction hash) at 100% coverage, so the schema does the work. The description contributes no additional parameter meaning such as accepted formats or chain scoping, which is the expected baseline.

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?

A precise verb+resource statement ('Decode an Ethereum transaction') plus the specific artifacts returned (function, args, amounts, ENS). An agent can tell it does calldata/log interpretation rather than the balance-listing of evm_transfers or the raw passthrough of rpc_call, though no sibling is named explicitly.

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?

Usage is implied by the purpose and heavily colored by the payment procedure (call, get challenge, retry with _meta["x402/payment"]), which is real operational guidance. However there is no statement of when to prefer this over evm_transfers, rpc_call, or txcheck_check, nor any exclusion or failure condition.

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