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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description reinforces this in domain terms an agent cares about ('never creates a checkout or spends money'), which is meaningful added context for a tool whose name suggests purchasing, but it stops short of disclosing computation limits or return format.

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 with zero filler; the core purpose is front-loaded and the read-only caveat is appended exactly where it prevents misreading the name as a purchase action.

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?

With no output schema and 0% parameter coverage, the description leaves the agent uninformed about what a 'plan' returns (pack breakdown, pricing, savings) and how serviceId should be formatted. Adequate to know the tool's intent, but not enough to call it confidently for a 2-required-param tool.

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 carries the burden, and it only loosely maps its two terms ('service', 'number of units') to serviceId and units. No identifier format, no guidance on what constitutes a valid service, and no detail beyond what the schema's types already show.

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 and resource: 'Plan the lowest-cost prepaid GXEON pack combination' scoped to a service and unit count. This reads clearly as an optimization/planning tool, distinct from the sibling list_* tools, though the description never names a sibling to sharpen that 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?

The scope ('for a specific service and number of units') and the clarifying 'never creates a checkout or spends money' imply when to reach for it versus a purchase flow, but no explicit when-to-use, prerequisites, or named alternatives are given.

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