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

Annotations already declare readOnlyHint and openWorldHint, but the description adds rich behavioral detail: signature sources (openchain.xyz with 4byte.directory fallback), the decoding strategy against each candidate, that bigints are returned as strings, and payment terms including $0.002 per successful x402 call with failed calls uncharged. This goes well beyond what annotations provide.

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?

The description is front-loaded with the core purpose, then adds sources, decoding behavior, output format, and pricing in compact sentences. Every sentence contributes useful information without repetition or filler.

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?

Given the output schema, 100% parameter schema coverage, and annotations covering safety, the description supplies the remaining context an agent needs: data sources, fallback behavior, decoding logic, bigint return format, and cost/charging semantics. No important detail for correct invocation 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 the schema already documents the data and selector parameters. The description reinforces the selector-vs-calldata input distinction but does not add substantial new parameter meaning beyond what the schema already supplies, so the baseline of 3 applies.

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?

The description states a specific verb (decode) and resource (EVM function selector/calldata), and it clearly explains what is returned: function signatures for a selector and decoded arguments for calldata. An agent can distinguish this from sibling execution tools like evm_call or evm_simulate 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?

Usage is implied by the input framing: use this when you have a 4-byte selector or calldata to decode. However, the description gives no explicit when-to-use, when-not-to-use, or alternative-tool guidance against siblings such as evm_call, evm_simulate, or encode.

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