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

Annotations already declare readOnlyHint and openWorldHint, but the description adds genuinely non-obvious behavior: cost of $0.002 USDC per successful call, x402 payment across Base/Solana/Arc, and no charge on failure. It does not cover rate limits or what a payment failure looks like, but the billing semantics are the key disclosure an agent needs.

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 sentences, front-loaded with the resource and returned fields, followed by the operational cost model. No filler or repetition, and every clause contributes either identification or calling context.

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?

An output schema exists and annotations cover the safety/read profile, so the remaining burden is billing and data-source context, which the description supplies. Only lingering gap is any hint about chain selection among the five supported chains, which lives solely in the schema.

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%, so both parameters are documented in the schema; the description only restates the 'by number or latest' behavior and never mentions the chain parameter (base/ethereum/arbitrum/optimism/polygon) or the default. Baseline 3 applies since the schema carries the semantic load.

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?

States a specific verb (retrieve) and resource (EVM block) and enumerates the returned fields (hash, time, tx count, gas used/limit, base fee), which makes it distinguishable from evm_tx, evm_logs and evm_contract. It stops short of explicitly naming the sibling to use for transaction-level data.

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?

There is no when-to-use / when-not-to-use guidance and no named alternative, despite a dense sibling set (evm_tx, evm_logs, rpc_evm, gas). The only usage-adjacent statement is that data is read over public RPC and that calls are billed, which is context rather than selection guidance.

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