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

Annotations declare destructiveHint=true, so the safety profile is already covered. The description adds genuinely non-redundant behavior: partial merge semantics and the non-obvious retire-via-end_at trick. It omits permission requirements and reversibility, keeping it at a 4.

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 plus an endpoint reference, front-loaded with the mutation semantics and the retire tip. No filler or restatement of the title.

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 14-parameter mutation with no output schema, the description covers the essentials: what changes, merge behavior, and a key edge case. Minor gaps remain around auth/account scoping (account_slug is only explained in the schema) and error behavior, but nothing an agent needs to invoke it is missing.

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 every parameter is already documented with type, format and examples (e.g. decimal string value, ISO 8601 datetimes). The description only groups fields conceptually ('validity window', 'attached releases') and adds no syntax or constraint detail beyond the schema.

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 ('Change'), resource ('an existing discount code'), and enumerates the mutable surface (code, value, quantity, validity window, attached releases), plus the underlying PATCH endpoint. An agent can immediately tell this apart from the create/get/list siblings.

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 a clear partial-update rule ('Only the fields you pass are sent') and a concrete operational recipe for the common retire case ('set end_at to now'). It does not name alternatives or explicit when-not-to-use conditions, 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.