x402_pay

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

With no annotations, the description carries full behavioral disclosure. It explicitly states that signing is LOCAL and non-custodial ('key never leaves this process'), explains the retry with X-PAYMENT header, details the return shape, and discloses error behavior ('errors cleanly (never mis-signs)'). It also highlights security tradeoffs (holding spending keys, env var protection, allowlist pinning). This is exemplary transparency.

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 a dense, single paragraph but is front-loaded with the core action and then structured into relevant sections (flow, supported chains, setup, safety, security). Every sentence conveys non-obvious information, and no content is filler. It could be slightly more scannable with line breaks, but the content justifies the length.

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?

Given 16 parameters and no output schema, the description covers all essential context: supported blockchains, key configuration per chain, return format, error semantics, security warnings, and safety mechanisms. It even explains how to create a walletId. The lack of an output schema is mitigated by explicitly specifying 'Returns { status, paid, body, settlement? }'. This is complete for a tool of this complexity.

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 the baseline is 3. The description adds value beyond the schema by explaining the shared env-var fallback pattern, the walletId vs address distinction, and the security rationale for params like allowedHosts and maxAmount. It references several params directly, but not all 16—though the schema descriptions already handle those. Overall it meaningfully enriches setup and intent without fully compensating for every param.

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 opens with a specific verb+resource+behavior: 'Fetch an HTTP resource and, if it returns 402 Payment Required, pay it automatically with x402 and return the paid response.' It clearly distinguishes from sibling x402_discover by focusing on the payment execution flow rather than discovery. The step-by-step breakdown of the 402 handling further reinforces a unique, well-defined purpose.

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 clear context for when to use the tool (on any 402-paywalled resource) and provides explicit guidance on configuration, supported networks, and safety controls. It notes that Tron/UTXO/etc. are 'UPCOMING' and return a coming-soon error, which implicitly tells users not to rely on those yet. It doesn't explicitly contrast with x402_discover, but the usage context is unambiguous and actionable.

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