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

No annotations are provided, so the description carries the burden: it discloses the exact algorithm, hex-as-bytes input handling, and payment requirement ($0.005 per call over x402/USDC). It hints that byte count is returned but does not fully define the response structure or error behavior, so it falls 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?

The description is front-loaded with the use condition and algorithm caveat, followed by exclusions and pricing. Every sentence contributes relevant selection or invocation guidance with no 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?

For a simple one-parameter hashing tool, the description covers invocation-critical context: algorithm identity, input interpretation, alternatives, and payment. Because there is no output schema, the only remaining gap is an exact return shape beyond the vague phrase 'with the byte count'.

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%, and the schema already documents that input is plain text or a 0x-prefixed hex payload to hash as bytes. The description restates input types but adds no meaningful syntax or format detail beyond the schema, so the 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 operation: Keccak-256 of a string or hex payload, yielding the digest the Ethereum chain would produce. It explicitly distinguishes itself from SHA3-256 and from sibling tools util_selector and util_sha256, so an agent can select it confidently.

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 explicit when-to-use guidance for Ethereum hashing that must match chain behavior, and explicit when-not-to-use cases for non-Ethereum file/API digests and function selectors. It names the alternative endpoints /v1/util/sha256 and /v1/util/selector.

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