Pay an x402 endpoint in USDC or $THREE and return its result

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

Discloses key behaviors: automatic payment settlement, two signing modes, bounded by max_usd and MAX_PAY_USD cap, refusal before money moves if over cap, confirmation requirement, and token override behavior. Annotations (destructiveHint=true) are consistent, and the description adds context beyond annotations.

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 concise (~150 words) and well-structured with clear separation of modes, tokens, and constraints. Every sentence adds value, and there is no redundancy or fluff.

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?

Covers main aspects of a payment tool but lacks details on return value format (no output schema) and error handling (e.g., what happens if payment succeeds but endpoint fails). Idempotency key is described in schema but not emphasized in description. Some gaps remain.

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%, so baseline is 3. The description adds some context (e.g., session_token overrides secret, token ignored when session_token, max_usd bounded by cap), but most parameter meaning is already clear from the schema.

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 calls a paid x402 endpoint, settles payment, and returns the result. It distinguishes itself from sibling tools (find_services, inspect_endpoint, x402_wallet) which are about finding, inspecting, or managing wallets, not executing paid calls.

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 provides explicit guidance on when to use self-custodial vs session-governed modes, which token to pay with (USDC or $THREE), and mentions caps and confirmation. However, it does not explicitly compare to sibling tools or state when not to use this tool.

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