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

With no annotations, the description carries the full behavioral burden and discloses two non-obvious traits: a per-call cost ($0.005) and a payment mechanism (x402/USDC). It also warns against the SHA3-256 mix-up, a meaningful correctness caveat. It stops short of stating the return format or error behavior, but for a deterministic hash the payment and distinction details are the salient additions.

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 core operation, then use cases, then pricing. Each clause earns its place and nothing is redundant.

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 single-parameter, no-annotation, no-output-schema tool, the description is largely self-sufficient: it states what the function is, when to use it, the SHA3-256 pitfall, and cost. The only minor omission is the output format (hex), which is reasonably inferable for a hash.

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 explains the single 'input' parameter as plain text or a 0x-prefixed hex payload hashed as bytes. The description's phrase 'any string or hex payload' reiterates rather than extends that, so the baseline 3 for high-coverage schemas 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 names a specific verb and resource ('Keccak-256 of any string or hex payload') and crucially distinguishes the operation from the near-identical SHA3-256, which an agent would otherwise confuse it with. It also identifies its domain (Ethereum hashing), letting it be told apart from siblings like util_sha256 without opening a 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?

It names concrete use cases (selectors, event topics, salts, CREATE2 addresses) that tell the agent when this tool applies. It distinguishes itself from SHA3-256 but doesn't explicitly route to adjacent siblings such as util_selector or util_sha256, so usage context is clear but not fully exhaustive.

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