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

With only destructiveHint=true provided, the description adds genuine behavioral context by disclosing two external dependencies (existing Stripe code, campaign coupon configured in dashboard) that would otherwise be unknown. It does not explain what happens if a code is re-assigned or whether the assignment is reversible, which limits it below a 5.

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 front-loaded sentences carry the purpose and the prerequisites with no filler; the trailing 'Rewardful: POST /v1/affiliate_coupons.' is a useful API anchor but slightly redundant overhead.

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 two-parameter create tool with no output schema, the description covers purpose, required external state, and the source endpoint. Missing only return-value and conflict/overwrite behavior, which are minor for an agent deciding whether to call it.

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% and the token property already documents 'the exact coupon / promotion code as defined in Stripe'. The description largely restates that constraint, adding little syntax or format detail beyond what the schema provides, 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?

The description states a concrete verb and resource ('Assign a coupon / promotion code to an affiliate') plus the business effect ('so sales using it are credited to them'), which clearly separates it from rewardful_create_affiliate_link and rewardful_create_affiliate. It never names a sibling, so differentiation is implicit rather than explicit.

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?

It supplies two real preconditions for use: the code must already exist in Stripe, and the affiliate's campaign must already have a campaign coupon set in the dashboard. That is strong when-to-use context, though no alternative tool or failure path is named for cases where those preconditions are unmet.

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