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

Annotations provide no safety hints (readOnlyHint, destructiveHint are absent), so the description carries the burden. It explicitly states 'This is read-only and moves no funds,' disclosing a critical behavioral trait. It also provides a concrete state summary (x402/Base-USDC live; MPP, AP2, etc. fail-closed) and the rationale (external provider/verifier not yet production-verified). This is strong behavioral disclosure beyond schema.

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, tightly packed with relevant information: it defines the scope (discovery, read-only), the resource, and the live/fail-closed states with reasons. Every clause earns its place; there is no filler or redundancy.

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 zero-parameter discovery tool with no output schema, the description covers the essential context: what it does, that it is safe (read-only), and what the current capability landscape looks like. An agent could call this tool with full understanding of its behavior and risks. The lack of an output schema is a minor gap, but for a capability-discovery tool the description suffices.

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?

The tool has zero parameters, and the schema covers 100% vacuously. The description adds no parameter-specific details because there are none to add. This is a no-argument capability discovery tool, so the description cannot meaningfully add parameter semantics; a baseline 4 is appropriate for the zero-parameter case.

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 that the tool 'discovers' payment capabilities and their 'truthful activation state' for a specific resource (MUJ428). It explicitly distinguishes itself from siblings like select_payment_rail by being read-only and not moving funds. The verb 'discover' plus the resource and scope make the purpose unambiguous.

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 conveys that this is for discovery (read-only) rather than for initiating payments, which is a critical usage distinction given siblings like select_payment_rail or invoke_trust_service. However, it does not explicitly name alternative tools or state when not to use it, leaving some inference required. The implicit guidance is clear but not fully explicit.

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