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

Adds genuinely useful context beyond the annotations: the key is used only for the call and not stored, and there is a per-call cost of $0.001 in USDC on Base via x402. This payment/auth requirement is exactly the kind of operational detail the annotations (readOnlyHint=false, openWorldHint=true) do not convey.

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?

Four short sentences, front-loaded with the operation and its options, followed by use case, privacy note, and cost. Every sentence carries distinct information with no padding.

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?

With no output schema, the description compensates by noting the results are produced in hex and base64. Combined with the privacy and payment details, an agent has enough to call it correctly; a precise return shape is the only minor gap.

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 schema already documents all three parameters including the algorithm options. The description restates the algorithm list and mentions output encodings, adding little beyond what the schema already provides, so the baseline 3 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?

States a specific verb (compute) and resource (HMAC of a message with a key), enumerates supported algorithms, and names the output encodings (hex and base64). An agent can distinguish this from the sibling hash tool 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?

Provides one concrete use case ('Use to check webhook signatures'), which implies context. However it never says when NOT to use it or routes to alternatives such as the sibling 'hash' tool, so selection between closely related tools is left to inference.

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