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

Beyond the annotations it discloses the auth requirement (Authorization: Bearer mo1_… or ref), the op_id replay window ('a repeat with the same op_id within 10 minutes answers the first result and never changes the order twice'), and field-level error behavior with per-country postcode rules. It does not say whether a call is a partial merge or replaces previously set checkout fields, which is the main behavioral gap for a 12-parameter mutation.

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?

Dense but front-loaded: purpose first, then field-by-field conditions, then error/auth/idempotency notes. Every clause carries information, though the single run-on paragraph would read better as short grouped sentences separating address, method, coupon and operational concerns.

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 12-parameter mutation with nested address objects, no output schema and no required fields, the definition covers what matters: valid value sources, auth, idempotent retry, and error feedback. It leaves open atomicity (does one bad field reject the whole call?) and the merge-vs-replace semantics of a partial call.

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 coverage is already 92%, so the baseline is 3, but the description adds real meaning: which values must be harvested from view_checkout (shipping_method id, payment_method key, saved address ids), that country is a two-letter code, that phone is mandatory, and that state/companynr/vatnr are optional-when-known. The one unexplained parameter is coupon_remove, undocumented in both schema and description.

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?

Opens with a specific verb and resource: 'Fill in the checkout of the order in one call', then enumerates exactly what can be filled (addresses, shipping/payment method, coupon, newsletter). It implicitly separates itself from view_checkout (the source of ids) and place_order (finalization), so an agent can tell where this sits in the flow.

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 concrete conditional guidance: shipping_address 'when delivery goes elsewhere', address ids 'when the shopper has saved addresses', newsletter 'only when the shopper asks for it', and states the order reference comes from start_order. It never states an explicit prerequisite sequence (call view_checkout first) or when not to call it before place_order, so it stops short of a 5.

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