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

Annotations only indicate readOnlyHint=false and no destructive/idempotent hints. The description goes beyond this by explaining that the checkout creation may also create or link a buyer account, that subscriptions complete in the browser, and that a UCP-Agent metadata is required. This adds transparency about side effects and prerequisites not evident from the annotations alone.

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 description is a single dense paragraph that packs in product IDs, pricing, metadata requirements, and return behavior. It is not broken into sections or bullet points, making it harder to scan, but it does front-load the main purpose and includes essential details without excessive redundancy.

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?

Given the tool's complexity (nested objects, optional fields, multiple product types), the description covers key aspects: it specifies the product ID formats, pricing logic, the requirement for ucp-agent, the effect of providing buyer.email, and the return object structure. This provides a solid overall picture, though it remains somewhat dense and could benefit from clearer separation of concerns.

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?

While the schema already provides full descriptions for parameter structures, the description enriches understanding by specifying the pricing for each product ID (e.g., 49 €, 79 €, 20 €), the condition that nota-simple is charged only with verified PDF, and the idempotency-key requirement for related operations. This extra context goes beyond the schema's basic format descriptions.

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 clearly states the verb 'Crea' (creates) and the specific resource 'sesión de checkout UCP', and lists the exact products it covers (informe de viabilidad, nota simple registral, suscripción de Subastech). It distinguishes itself from sibling tools like update_checkout, complete_checkout, and cancel_checkout by focusing on creation.

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 does not explicitly mention when to use this tool versus the sibling tools (e.g., update_checkout, complete_checkout). It only describes its own function without naming alternatives or providing conditions for choosing among them, leaving the selection to inference.

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