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

Annotations already declare readOnly, idempotent, openWorld, so the safety profile is covered; the description adds real behavioral context beyond that — live unpaid probes returning valid x402 terms, OFAC screening of payTo, top-3 pre-checking, and a 1-credit-per-successful-call cost model. The credit/header paragraph is genuinely useful operational detail, though the referral program text is monetization marketing rather than behavior of this call.

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 purpose is correctly front-loaded in sentence one, but the majority of the text is a prepaid-credit pitch and a referral revenue-share program (20% of net revenue, off-chain ledger, monthly settlement, manual review, min 1 USDC, earnings endpoint) that does not help an agent select or invoke this tool. That material belongs in docs, not the tool definition.

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?

With an output schema present and full parameter coverage, the return values need not be explained, and the ranking/credit behavior is covered. However, the description leaves the non-prepaid path ambiguous ('No demo limit with prepaid credits' implies a limit exists without them, but never states what it is or what happens on 402/credit exhaustion), while spending space on referral details.

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 schema already documents task, limit, network, and maxPrice, establishing a baseline of 3. The description adds nothing about parameter meaning — it never clarifies accepted CAIP-2 network formats, how maxPrice interacts with ranking, or what a higher limit costs in credits.

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 opening sentence gives a specific verb and resource: 'Find which x402 paid service to call for a task', and the second sentence names the ranking signals (relevance, liveness, latency, price). It stops short of differentiating from siblings such as x402_precheck and x402_gateway_plan, even though 'top 3 freshly pre-checked' gestures at the relationship without explaining it.

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?

Usage is only implied: an agent can infer this is the discovery step before paying a service, but there is no explicit when-to-use versus x402_precheck, x402_verify_settlement, or x402_gateway_plan. No exclusions or prerequisites for calling it are stated beyond the credit/header mechanics.

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