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

Goes well beyond the annotations by disclosing the price (0.10 USDC on Base), the exact two-step x402 flow, where the proof goes in params._meta, that a legacy base64 argument is also accepted, and that signing occurs in the caller's wallet. It also sets honest expectations that payment does not guarantee approval, traffic, ranking, or safety — non-obvious behavior an agent cannot get from readOnlyHint=false / idempotentHint=false.

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 first sentence front-loads the action and the second the expectation-setting caveat, with payment mechanics bracketed off so they can be skipped by a reader who only needs intent. The bracket block is dense but every clause (price, flow, fallback argument, signing location) carries operational weight — one sentence about rejection reasons or moderation timing would have been the only justified addition.

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?

An output schema exists so return values need no explanation, and the description covers the cost, the payment protocol, and the no-guarantee caveat — the three things most likely to trip an agent on a paid write. It stops short of saying what happens after submission (review/moderation, listing latency, duplicate handling for an agent already listed), though that is secondary to correct 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 earns a bump because it explains payment mechanics that the schema only hints at — the schema documents _x402_payment while the description reveals the preferred _meta['x402/payment'] transport and when each applies. The other listing fields (name, tags, agent_card_url) are left entirely to the schema.

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?

States a specific verb and resource — 'Submits a public directory listing for an agent the caller owns' — which disambiguates the otherwise confusing name 'list-agent' (submission, not enumeration). The ownership scope ('an agent the caller owns') further separates it from ontario_list-service, the sibling for a different resource type.

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 procedural guidance for the payment handshake (call without payment, then retry with the signed payload) and notes validation is free, which is useful when-to-call context. However, it never states when to choose this over siblings like ontario_refresh-listing for updates or ontario_validate-agent for pre-checks, so alternative routing is left to inference.

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