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

The annotations already declare readOnlyHint=true, and the description reinforces this by explicitly disclaiming payment execution, card charges, and fund movement. It adds real value beyond the annotation by explaining the approval workflow and the single-use, exact-match TGA prerequisite for downstream execution. It stops short of describing rate limits or how the draft payload is keyed to a session.

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?

Three tight sentences: purpose and return artifact first, then the safety boundary. Nothing repeats structured data and nothing is padding.

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?

No output schema exists, so it is important that the description names the return value, which it does ('AP2/x402 checkout payload draft'). The safety boundary is also covered, making this sufficient for a non-destructive preparation tool; only the undocumented parameters keep it from being complete.

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 0% and the description never mentions offer_id, quantity, or currency. Only a loose hint exists that the item is a 'catalog item', leaving the agent to infer that offer_id is a catalog offer identifier and that quantity/currency shape the proposal. With three undocumented parameters, this is a clear gap.

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 ('Prepare a purchase proposal for a catalog item') and names the concrete artifact returned ('AP2/x402 checkout payload draft'). It is clearly a pre-payment step, but it never distinguishes itself from the sibling codex_quote_request, which sounds like a neighbouring operation an agent could easily confuse it with.

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 implies usage via 'for human approval' and 'execution happens only through the isolated financial connector gateway', which tells the agent this is the pre-execution stage. However, it gives no explicit when-to-use versus codex_quote_request or codex_catalog_get_product, so routing between siblings 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.