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

readOnlyHint=true already covers the safety profile, so the description's contribution is payload shape: it discloses that a plan comes bundled with its selling plans including delivery policy, billing policy, anchors and discounts. That is meaningful context about what actually comes back, though it says nothing about not-found behavior or expansion options.

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?

One sentence, front-loaded with the verb and resource, and the parenthetical enumerates return contents without padding. Nothing extraneous.

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 with full schema coverage, readOnly annotations and no output schema, the description gives enough to call it correctly and sets expectations about the nested selling-plan payload. Only minor gaps remain (error/empty behavior).

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 single plan_id parameter is documented with its accepted integer/string forms and a provenance hint (from recurpay_list_plans). The description adds no format or constraint detail 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+resource ("Get one plan") with a scoping qualifier ("one") that implicitly separates it from recurpay_list_plans, plus the nested selling-plan contents are enumerated. It stops short of naming the sibling explicitly, so an agent must infer the list/get split.

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: retrieving a single known plan. There is no explicit "use this when..." statement, no exclusion (e.g. "for browsing all plans use recurpay_list_plans"), and the pointer to recurpay_list_plans lives in the schema param text rather than the description.

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