x402_discover

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

With no annotations, the description carries the full burden and succeeds. It discloses that the call is 'PUBLIC: needs no API key, no wallet and spends nothing, so it is always safe to call,' and warns that `amount` is in ATOMIC units (with a conversion example). These are behavioral traits beyond what the schema/annotations convey, essential for an agent to safely invoke the tool.

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 moderately long but each sentence earns its place: purpose, sibling differentiation, return structure, atomic-unit caveat, safety, and filtering/pagination guidance. It is front-loaded with the main purpose and flows logically. No redundancy or filler.

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 the absence of an output schema, the description fully compensates by detailing the return shape ({ resources: [...], pagination: {...} }), explaining atomic unit conversion, and noting safety. It also covers filtering and pagination usage. For a moderately complex tool with no annotations or output schema, this description is comprehensive enough for correct selection and invocation.

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 baseline is 3. The description mentions 'Filter with `type` (e.g. "http") and page with `limit`/`offset`,' but this largely restates the schema descriptions and adds minimal new meaning. It does contextualize parameters in the workflow, but doesn't go beyond what the schema already provides, so it remains at baseline.

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's purpose: 'Discover x402-gated APIs you can pay for — browse the facilitator's Bazaar catalogue of registered x402 resources.' It uses a specific verb ('Discover') and resource, and explicitly distinguishes from its sibling x402_pay by noting that the pay tool only fetches a URL you already have, making this the only way to locate a paid endpoint independently.

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?

It gives explicit guidance: 'Use this BEFORE x402_pay whenever you need to FIND a paid endpoint rather than call one you were already given.' It also provides follow-up direction ('Then pass a chosen `resource` URL to x402_pay') and clarifies exclusions (when you already have a URL, use pay instead). This fully covers when-to-use and alternatives.

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