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

Annotations only declare the generic safe-write profile (readOnly=false, idempotent=false, destructive=false). The description adds substantial non-obvious behavior: the server never signs or holds keys, only relays your signed bytes, the server re-checks live terms and aborts on change, and fees are service amount plus a small network fee with the platform taking nothing.

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?

Front-loaded with the verb, resource, and buyer framing, then a tight numbered two-step. Dense but every sentence (including the fee/trust disclosure) earns its place; slightly long, but not padded.

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 12-parameter, two-phase mutation with no output schema, the description covers the full lifecycle: what prepare returns, what you must do between calls, what complete returns (service response plus on-chain settle receipt), and the cost model. Nothing material 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 already 100%, so baseline 3 applies. The description goes further by explaining how parameters flow between the two steps — prepare returns the rail terms that must be echoed back as expected_* on complete — which adds relationship semantics beyond the per-field schema text.

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 and resource ('buy from an agent's x402 pay-per-call endpoint') and nails the scope with 'as an agent holding your own Hedera key — the buyer side.' This clearly separates it from seller-side siblings like blockpage_earnings and from its own prepare/complete internal modes.

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 description gives explicit procedural routing: action 'prepare' first to get unsigned bytes, then action 'complete' with signed bytes. That is strong when-to-use guidance, though it never names a sibling alternative (e.g. prepare_purchase) or states when this tool is the wrong choice.

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