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

The readOnlyHint=true annotation already tells the agent this is a safe, non-mutating lookup, and 'Fetch' is consistent with that. The description adds the API endpoint reference but says nothing about error behavior for missing ids or the shape of the response, so it only marginally exceeds the annotation baseline.

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 short sentences with the action and resource front-loaded and zero wasted text. The endpoint reference is compact and informative rather than padding.

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 single-parameter read tool with no output schema and annotations covering the safety profile, the description supplies everything needed to invoke it correctly. Only minor gaps remain around failure modes for invalid ids.

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% and the single coupon_id parameter is fully documented as a UUID in the schema. The description adds no format, constraint, or sourcing detail beyond what the schema already provides, so the baseline of 3 applies.

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?

The description states a specific verb and resource ('Fetch a single affiliate coupon by id') and notes the underlying endpoint, which distinguishes it from the sibling list_affiliate_coupons by the singular 'single' and the id-based lookup. It is clear without needing the schema, though it does not explicitly name the sibling it complements.

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?

There is no when-to-use guidance, no statement of prerequisites (e.g. needing a valid coupon id), and no contrast with list_affiliate_coupons or other retrieval tools. The 'by id' phrasing implies the caller already holds an id, but that is left to inference.

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