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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description adds valuable behavioral context: the operation is deterministic, paid ($0.001 USDC), and JWT decoding is non-verifying. This goes beyond the annotations by disclosing the payment side effect and a specific nuance of the JWT operation, though it doesn't detail settlement requirements or failure modes.

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 description is two sentences with no filler. It front-loads the fee and operation list, then adds the x402 settlement detail. Every word contributes to agent understanding, making it concise and well-structured.

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?

An output schema exists, which reduces the need to document return values. The description covers the operation set and payment context, but it lacks guidance on selecting this tool over free sibling alternatives and does not specify parameter nuances for this multi-operation tool. For an agent facing many similar tools, this is a notable completeness 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 description coverage is 0%, so the description must compensate. It names the operations, which maps directly to the `operation` enum, and implicitly ties `secret` to HMAC-SHA256. However, it does not explain input format expectations (e.g., Base64 decode input, JWT string format) or clarify when `secret` is required vs ignored, leaving notable semantic gaps.

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?

The description clearly states the tool performs paid hashing/encoding operations (SHA-256, SHA-512, HMAC-SHA256, Base64, JWT decode) and mentions the payment mechanism. It is clear what it does, but it does not explicitly differentiate itself from the many sibling single-operation tools (e.g., sha256, base64_encode) beyond the payment aspect, so it stops short of full sibling distinction.

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 only usage context is that x402-aware MCP clients can authorize and settle inside the call, implying this is for payment-integrated workflows. There is no explicit guidance about when to choose this combined tool over the free siblings, nor any 'when not to use' or alternative recommendations. An agent is left to infer when the paid bundle is preferable.

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