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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint, so the safety profile is covered; the description adds the cost ($0.003 per call), the accepted rails (USDC on Arc/Base/Solana, XNT on X1), and the two-step terms-then-pay handshake — all context annotations cannot express. It also warns that a live endpoint check runs against every listed endpoint, hinting at latency and side effects. It does not state what happens if a payment payload is invalid or expired, which is the main remaining gap for a paid 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 payload contents are front-loaded in the first sentence and the payment mechanics follow in the last. The clause 'The registry is new, so the list is short and says so' is marginally self-referential padding, though it does set a useful expectation about result volume.

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 one optional parameter, no output schema and permissive annotations, the description carries everything the schema cannot: what each record contains, that endpoint checks are live, what it costs, on which chains, and the payment handshake. An agent can invoke it correctly on either the free-terms call or the paid call without further information.

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% and the `payment` property is already well documented as a base64 x402 payload. The description still adds real meaning beyond the schema by explaining the negotiation loop (fetch terms unsigned, sign, resubmit) and thereby conveying that omitting the parameter is a valid, intentional first step rather than an error.

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 uses a specific verb-plus-resource framing ('The X1 Agent Registry in full: every registered agent...') and enumerates exactly what the payload contains: owner, registration file, live endpoint checks across MCP/A2A/x402/web, payability on X1, and feedback counts. That level of specificity distinguishes it from registry-adjacent siblings like arc_agent_search or agora_list without needing to open either schema.

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 an explicit, actionable procedure for the paid path: 'Call once without `payment` for the terms, sign them with your own wallet, call again with `payment`.' That is genuine when-and-how guidance for the parameter. What is missing is routing versus alternatives — it never says when to prefer this full dump over a targeted lookup like arc_agent_search or find_mcp_or_api.

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