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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuine behavioral context by enumerating what the comparison actually surfaces (price, data, network, speed, contract, inclusions), which goes beyond the annotations. It does not mention failure behavior for invalid plan references.

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 sentences, no filler. The what-and-why (compare on these axes) comes first, and the how (pass these identifiers) follows, matching the order an agent needs them.

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?

An output schema exists, so return-value shape need not be described. For a single nested-array parameter tool with annotations covering safety, the description supplies everything needed: comparison scope, required identifiers, their source, and the cardinality bound.

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 largely succeeds: it names the three per-plan fields (plan type, provider slug, plan slug) and tells the agent where those values originate. It also conveys the 2-4 cardinality that the schema enforces via minItems/maxItems. It does not spell out the plan_type enum values, though the schema exposes them.

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 (compare) and resource (plans) plus the exact comparison axes: price, data, network/technology, speed, contract, inclusions. This is clearly distinguishable from get_plan (single plan) and search_plans (discovery), so an agent can select it without opening other schemas.

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?

Gives a concrete workflow cue by telling the agent to pass values 'as returned by search_plans', which implies search_plans must run first. It stops short of stating when not to use this tool (e.g., for a single plan use get_plan), so it is clear but not exhaustive.

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