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

Annotations already declare readOnlyHint=true, so the safety profile is covered; the description adds real behavioral context by disclosing the returned fields, pagination behavior, and the underlying GET /coupon call. It doesn't cover rate limits or default page size behavior beyond what the schema states.

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?

Compact and front-loaded, with the resource and returned fields leading. The phrase 'Filterable fields: none documented' is slightly awkward but earns its place by heading off filter attempts.

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 simple read-only list tool with no output schema, the description is reasonably complete: it names returned fields and explains pagination. It could say more about the default page size interplay, but nothing essential for a correct call 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 limit, order, offset, and filters are already fully documented. The description adds only the pagination hint ('pass next_offset as offset'), which is marginal and slightly at odds with the schema's naming. Baseline 3 applies when the schema does the heavy lifting.

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 (List) and resource (coupons), and enumerates the returned fields (code, description, type, enabled, linked discount item), which clearly differentiates it from list_contacts, list_invoices, etc. It stops short of explicitly contrasting with siblings, but the resource is unambiguous.

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 establishes when filtering is not useful ('Filterable fields: none documented; the list is small') and how to page, which is genuine usage context, but gives no explicit when-to-use/when-not guidance or alternative tools. Adequate but with clear gaps.

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