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

Annotations declare the write/safety profile (readOnlyHint=false, destructiveHint=false), and the description adds genuinely new behavior: the returned cart_token's downstream use and the external handoff where the person pays on macron.lt. It stops short of disclosing cart lifetime/expiry or whether a prior cart is reused or replaced.

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?

Two tight sentences with zero filler, front-loaded with what the tool does before describing its outputs and their intended recipients. Every clause carries actionable information.

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 no output schema, the description takes on the return-value burden and covers the two key fields (cart_token, checkout_url) plus the external payment step. It omits secondary details such as cart expiration or error cases, leaving a small but real gap.

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?

The tool takes zero parameters, so per the rubric the baseline is 4. There is nothing for the description to clarify, and it correctly spends no words on inputs.

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 ("Creates an empty cart") and scopes it as empty, which distinguishes it from sibling cart mutators like add_line and set_quantity. An agent can identify this as the cart-initialization entry point 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?

Strong implied routing: the cart_token is flagged as needed "for the other cart tools," which tells the agent this must be called before get_cart/add_line/set_quantity/remove_line. It does not, however, state any explicit when-not condition or name an alternative entry point, so it falls just short of full usage guidance.

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