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

With no annotations, the description carries the burden and does disclose meaningful traits: both return encodings (hex and base64) and the cost/payment model ($0.005 per call over x402 USDC). It omits error behavior and input-normalization edge cases, but for a deterministic pure function that is a minor gap.

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 short sentences, front-loaded with what the tool does and its outputs, followed by use context and pricing. No filler or repetition.

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?

There is no output schema, so the description usefully supplies the return format (hex and base64) and the payment requirement, which an agent needs before calling. Only edge-case behavior (invalid hex, empty input) is unspecified, leaving it slightly short of fully complete.

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 single parameter already documents the 'plain text or 0x-prefixed hex' semantics; the description's 'any string or hex payload' merely paraphrases it. Baseline 3 is appropriate when the schema does the heavy lifting.

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 (SHA-256 hashing) and the input/output formats (hex and base64). Explicitly positions itself against the sibling util_keccak256 by noting it is 'the hash everything outside Ethereum uses', so an agent can disambiguate 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?

The Ethereum/non-Ethereum framing gives clear context for when to pick this over util_keccak256, and the listed use cases (file digests, API signatures, content addressing) reinforce that. It stops short of an explicit 'use util_keccak256 for Ethereum payloads' instruction, so it is strong but not fully prescriptive.

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