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

Annotations already cover the safety profile (readOnlyHint=true), so the bar is low. The description adds real value by disclosing the payload contents (campaign, links, coupon, visitor/lead/conversion counts) that an agent would otherwise not know without an output schema. Error behavior for a missing id is not addressed.

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: the operation and its returned scope come first, and the endpoint reference is appended as supporting metadata. No filler.

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 annotations carrying the safety profile and no output schema, enumerating the returned fields is the key missing piece and it is provided. Minor gaps (not-found/error behavior, naming the list alternative) remain.

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 parameter is fully documented as a UUID. The description only restates 'by id', adding no format, validation, or lookup semantics beyond the schema, so the baseline 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?

Specific verb and resource ('Fetch a single affiliate by id') with scope, plus a REST endpoint mapping. It implicitly contrasts with list_affiliates by saying 'single ... by id', but it never names the sibling explicitly, so it falls short of a 5.

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 only implied: 'single affiliate by id' suggests use when you already have an id rather than needing a filtered list. There is no explicit when-to-use, when-not-to-use, or named alternative (e.g., list_affiliates for browsing).

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