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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), and the description adds substantial operational context beyond them: a 2 KB input cap, a 400 on overflow that is never billed, and per-call pricing with the payment protocol and supported chains. This is exactly the extra context annotations cannot carry.

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 tight sentences, front-loaded with purpose, then limits, then cost. Every clause carries an actionable fact with no padding 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?

For a pure-function tool with an output schema present, the description need not explain return values, and it covers input limits, error behavior, supported algorithms/encodings, and billing. Nothing an agent needs to invoke it correctly is missing.

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%, so the baseline would be 3, but the description adds genuinely useful meaning: it maps keccak256 to 'the Ethereum hash', clarifies utf8 vs hex byte interpretation, and specifies the output is returned as both hex and 0x-hex. That goes beyond the schema enum labels.

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 (returns a hash) plus the exact algorithms and encodings it produces, and frames the scope as something the agent should not compute itself. An agent can immediately tell what this tool returns versus every sibling in the list.

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 opening sentence gives a clear condition for use ('when an agent needs a hash it should not compute itself'). It does not name an alternative or state when-not to use, but no sibling overlaps this function, so the routing gap is minor.

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