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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), yet the description adds substantive behavior: the call itself does not return data but a paid x402 request (GET /evm/block, $0.001 per call) that must be redeemed with an x402 or MPP client, and bad input is refused before any charge. That second-call and billing behavior is exactly the kind of context annotations cannot convey.

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?

One dense but well-ordered paragraph: purpose, returned fields, redemption mechanics, pricing, then error handling. Every sentence carries information, though the chain enumeration is redundant with the schema and could be trimmed.

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 well by explaining that the return is the exact paid request plus a response schema and example. An agent knows what it gets, what it costs, and the follow-up step needed; only the pagination/error envelope details are left implicit.

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 are already documented, including the decimal/0x-hex format and the default. The description restates the five chains and 'latest or a given number', adding no syntax or constraints beyond the schema. Baseline 3 is appropriate.

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 and resource ('a block header') and enumerates the exact chains and fields returned (hash, parent, timestamp, miner, gas used/limit). This cleanly distinguishes it from evm_transaction, evm_receipt, evm_code and evm_nonce without opening any schema.

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?

Opens with an explicit when-to-use ('Use when you need a block header on Base, Ethereum...') and scopes the input to 'latest or a given number'. It gives clear context but never states when-not to use it or names an alternative sibling, so it stops short of the top tier.

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