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

Annotations declare the safety profile, but the description adds the crucial trait they cannot express: a $0.001 USDC on Base charge via x402 per successful call. That cost side-effect also rationalizes the otherwise odd readOnlyHint=false / idempotentHint=false, since repeated calls incur repeat payment. It does not state the output encoding, keeping it at 4.

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?

Three front-loaded sentences with no filler: purpose first, use case second, cost last. Slightly denser than necessary but every sentence carries information an agent needs.

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?

No output schema exists, but a hash's return (hex digest) is self-evident from the name, and the payment requirement is fully disclosed. The only minor gap is not stating the output format or length explicitly, which is acceptable for this tool.

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 coverage is 100% and the single `text` parameter is already documented as accepting text or 0x-prefixed hex bytes, so the schema does the heavy lifting. The description reinforces the dual-input mode and adds the 0x-hex use cases, but contributes no syntax or format detail beyond the schema.

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 ('Keccak-256 hash') and pins down the exact variant versus generic siblings like hash and hmac. It also names the concrete domain (function selectors, event topics, storage slots), so an agent can distinguish it from other hashing tools immediately.

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?

'Use when building or decoding EVM calls' gives clear positive context for selection. It stops short of explicitly contrasting with the generic `hash` sibling or stating when a different hash is preferable, so it is a strong 4 rather than a 5.

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