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

Goes well beyond the annotations (readOnlyHint=false, openWorldHint=true, destructiveHint=false) by disclosing that it mutates later invoices, that coupons must match the subscription's plan, the one-fixed/one-percentage default limit, the confirmation-by-default requirement, and the API-key/auth need. The effect-on-invoices warning is exactly the kind of consequence an agent needs before invoking.

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?

Purpose is front-loaded and most sentences carry distinct value. There is mild redundancy in the two confirmation statements ('you confirm each call' and 'confirm with the user before each call'), which slightly dilutes an otherwise tight description.

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?

No output schema exists, but the description covers the return ('the full list') and the key operational constraints (coupon eligibility, per-subscription limits, confirmation, auth). Little an agent needs before calling is missing; only explicit alternate-tool routing is absent.

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 100%, so both parameters (coupon, subscription_id) are already documented in the schema with examples and sourcing hints. The description adds no syntax or format detail beyond the schema, so the baseline of 3 is appropriate.

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+resource ('Add a coupon to a subscription') plus behavioral scope ('adds to existing coupons, returns full list'). An agent can distinguish this from siblings like chargebee_change_subscription_plan or chargebee_cancel_subscription 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?

Offers implied context — a coupon can be added at any point in the billing cycle, and the plan/one-fixed-one-percentage constraints hint at when it applies. However, it never names an alternative tool or states explicit when-not-to-use conditions, so routing guidance is inferred rather than stated.

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