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

With no annotations, the description carries the full burden and does so well: it discloses both output encodings returned, that no API key or account is required, and the cost ($0.005 per call paid over x402 in USDC). These are the auth/pricing/return-shape facts an agent needs before invoking a paid endpoint.

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 use case and the Keccak-256 exclusion are front-loaded, and every clause is substantive. It is a single dense sentence chain with colon-stacked detail (output forms, pricing), slightly heavier than needed but nothing is 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 one-parameter tool with no annotations and no output schema, the description supplies the return encodings, the auth/payment model, the cost, and the sibling boundary. An agent has everything needed to call it correctly and interpret the result.

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% on the single parameter, so the baseline applies. The description's mention of 'any string or hex payload' mirrors the schema's 'Plain text, or a 0x-prefixed hex payload to hash as bytes' without adding format details, length limits, or encoding nuance beyond it.

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 of any string or hex payload) and specifies the output forms (hex and base64). It also explicitly distinguishes itself from the sibling util_keccak256 by naming the Ethereum hashing difference, so an agent can tell them apart without opening either 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?

Gives the triggering conditions explicitly (proving byte-for-byte equality of two payloads, or signing an API request) and includes a hard exclusion with the alternative named: 'Do not use for anything Ethereum hashes: the chain uses Keccak-256 (/v1/util/keccak256)'. Both when-to-use and when-not-to-use are present.

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