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

With no annotations, the description carries the full burden. It usefully discloses that no API key is required and previews the return shape ({id, status, currency, line_items, totals, ap2}), but says nothing about session lifetime, idempotency, failure modes, or what 'ap2' signifies. Partial disclosure of a mutation tool's behavior.

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 compact clauses, front-loaded with the core action, then the auth note, then the return shape. No filler sentences.

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?

For a creation tool with no annotations and no output schema, the description supplies the return shape and auth hint, which covers a lot. However, session lifecycle, required preconditions, and the meaning of buyer/context/cloud remain undocumented, leaving real gaps.

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 only 60%, and the description adds little beyond restating the cart shape: 'multi-item' maps loosely to line_items and 'mixed-currency' to currency. The buyer, context, and cloud (merchant token) parameters get no semantic explanation in either the description or 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 ('Create a UCP checkout session') with scope qualifiers ('multi-item, mixed-currency cart', 'for a merchant catalog'), which clearly separates it from the get/cancel/complete checkout siblings. It does not explicitly name an alternative, so it stops short of the top band.

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?

There is no guidance on when to choose this over uxc_get_checkout, uxc_complete_checkout, or uxc_search_catalog, nor any stated preconditions (e.g., must line_items reference existing catalog items). The 'No key' fragment hints at an auth mode but is not framed as usage guidance.

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