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

Annotations only declare readOnlyHint/openWorldHint/destructiveHint=false; the description goes well beyond them by disclosing the downstream consequences (Atom provisions a buyer account, the domain lands in the buyer's account, an account-claim email is sent post-payment) and operational constraints (the pay_url serves a real HTTP 402 challenge, hand it directly to the pay tool, never recompute the price). These are exactly the side effects an agent cannot infer from a readOnlyHint.

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?

Front-loaded with the core action and the sibling exclusions, then transitions to operational cautions; every sentence carries content. The first sentence is long with nested parentheticals and a mid-sentence alternative reference, which slightly hurts scannability for a tool an agent must select quickly.

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, the description needn't document return values, and it instead covers the pieces an agent genuinely needs: prerequisites, account ownership flow, post-payment notification behavior, and how to hand off the pay URL. Nothing required to invoke it correctly is missing.

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 all ten fields including the buyer_email ownership semantics and the ISO country format. The description reinforces that the buyer email must be the real end buyer rather than the agent platform, but that meaning is already present in the buyer_email schema description, so added value is marginal over the 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?

States a specific verb and resource (get a payable MPP pay link to register a fresh domain) and immediately scopes it against two siblings: it excludes curated Atom marketplace listings (directing to get_domain_purchase_pay_link_guest) and excludes OAuth-authenticated sessions (directing to get_domain_register_pay_link). An agent can pick this tool out of a 21-tool sibling list without opening any 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?

Gives explicit gating conditions: use ONLY when (a) the session has no authenticated Atom connection and (b) an MPP-native agent's payment tools are available, with the preferred alternative named for each failure case. Both the positive trigger and the exclusions are spelled out rather than implied.

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