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

Annotations already declare readOnlyHint=true, so safety is covered; the description adds real value by disclosing the curation filter (only publicly visible, still-active codes) and the important caveat that returned promotions may not apply at checkout due to revalidation of eligibility and stacking. Return shape and pagination remain undocumented.

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?

Three tight sentences, front-loaded with the scope constraint followed by filter optionality and the checkout caveat. No filler, though the final caveat sentence could have been folded in more economically.

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?

The read-only nature is annotated and the scope/caveats are explained, but with no output schema the description says nothing about what a promotion record contains or how results are ordered or bounded. For a simple two-optional-param list tool it is adequate, but an agent still cannot anticipate the response.

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 0%, so the description has to carry weight; it names both parameters conceptually ('product and billing-cycle filters are optional') and confirms they are non-required. It adds no meaning about what a productRef refers to or how billingCycle constrains results beyond the enum already in the schema, so compensation is only partial.

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 clear verb and resource ('List ... promotion codes') and narrows scope precisely to codes 'explicitly curated for public MCP visibility and still active in current DotMoose commerce data.' That scope language distinguishes it from any general promotion lookup, though none of the listed siblings are close enough for explicit contrast.

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?

Implies when the tool is appropriate ('optional' filters, curated public codes) and warns that 'First-party checkout revalidates final eligibility and stacking,' which hints the result is not authoritative for pricing. However, it never says to use quote_public_product or quote_domain for binding prices, so the routing 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.