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

Goes well beyond destructiveHint=true by disclosing concrete side effects ('may create an invoice / return a payment URL') and the response shape including required_action, which signals possible 3DS/SCA flow. It does not cover idempotency, repeated-attach behavior, or error conditions for a destructive billing operation.

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 compact sentences with the mutation warning and the resource front-loaded, then the endpoint and return shape. Nothing is padded or repeated from the schema.

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 10-parameter destructive mutation with no output schema, the description supplies the return fields and the key side effect (invoice/payment URL) an agent needs. It leaves gaps around checkout flow branches (redirect_mode vs invoice_mode) and failure handling, but the essentials are present.

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 100%, so the schema already carries meaning for all 10 parameters, and the baseline 3 applies. The description adds no parameter-level nuance such as how redirect_mode interacts with invoice_mode or what customize overrides are permitted.

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 ('attaches (subscribes) a plan to a customer') and front-loads the MUTATES marker, which implicitly separates it from the read-only sibling autumn_preview_attach. It stops short of naming that alternative explicitly, so differentiation is inferred rather than stated.

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?

Usage is implied by the verb and the 'subscribes' gloss, but there is no explicit guidance on when to choose this over autumn_preview_attach, nor any prerequisite such as the plan needing to exist first. An agent still has to infer the when-not condition from the MUTATES banner.

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