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

Annotations already declare readOnly/idempotent/openWorld/non-destructive, and the description adds genuinely non-structured behavior: cost ($0.003/call, 10 free/day), the x402 payment-required result after the free tier, and error semantics ('returns isError with a message for invalid input or upstream failure (not charged)'). This is exactly the extra context the 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?

Front-loaded with the value proposition and then labeled with 'When to use:', 'Price:', and 'Errors:' for easy scanning. The opening sentence is a long comma-separated list, but every clause earns its place; no padding.

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 so return values needn't be explained, and the description still covers scope, alternatives, cost model, and failure behavior. Nothing an agent needs to select and call this correctly is missing.

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 fully documented in the schema, and the pattern/default/enum are all present there. The description implies the hash input but never mentions the 'chain' selector, so it adds little 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+resource ('Any EVM transaction in plain terms') and enumerates exactly what is decoded: status, from/to, value, fee in native and USD, method, and ERC-20 transfers with symbols/amounts. It also explicitly distinguishes itself from the sibling tx_explain (which handles Solana signatures).

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?

Gives an explicit when-to-use rule ('For 0x hashes') and names the alternative plus the condition that selects it ('for Solana signatures use tx_explain'). Nothing is left to inference, and it goes further by documenting pricing/free-tier behavior.

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