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

Annotations already flag this as a destructive, non-idempotent, open-world write. The description goes beyond them by disclosing the downstream effect ('changes what the subscriber pays on the next billings') and imposing an explicit user-confirmation step, which an agent would not infer from the hints alone. It stops short of saying whether removal is reversible or how proration is handled.

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?

One front-loaded sentence carrying the verb, resource, and blast radius, followed by a short imperative precondition. No filler, no repetition of schema fields.

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 3-required-param mutation with full schema coverage and a complete annotation set, the description covers what it must add: it is a write, it affects future billing, and confirmation is required. Only minor gaps remain (behavior when removing a code that is not applied, whether a response body is returned).

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%: the 'action' enum, the 'code' example (TEST20) and the 'subscription_id' provenance (from recurpay_list_subscriptions) are all documented in the schema. The description only restates the general subject matter and adds no syntax, format or edge-case meaning beyond it.

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?

Specific verb pair ('add or remove') plus a concrete resource ('a discount code (coupon) on one subscription') and the effect on future billings. The 'WRITE:' prefix immediately separates it from the read-oriented siblings like recurpay_get_subscription or recurpay_list_subscriptions, and no sibling covers coupons at all.

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?

The description scopes usage to a single subscription and adds a precondition ('Ask the user to confirm'), which is useful operating guidance. However it never states when to choose add vs remove in context, nor does it mention any exclusion or alternative tool for coupon-related workflows.

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