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

readOnlyHint=true already tells the agent this is a safe read. The description adds only content scope ('line items', 'plan they pay stub for') and no behavioral context such as whether the subscription is current, whether line items are historical, or whether anything is paginated. With annotations covering the safety profile, a 3 is appropriate.

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?

A single sentence that front-loads the resource before listing the alternatives — good structure with no padding. It loses a point because the 'stub subscription / the plan they pay stub for' repetition is confusing rather than economical.

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?

There is no output schema and no parameters, so the description is the only source for what comes back, and it only vaguely gestures at 'subscription / billing line items' without describing the shape (plan, price, line items, period). Complexity is low, but for a no-schema read tool the return scope should be pinned down better than 'stub subscription'.

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?

The tool takes zero parameters (empty schema, nothing required), so there is no parameter semantics for the description to clarify. Baseline 4 applies — there is simply no gap to fill.

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?

The resource is identifiable — the business's subscription/billing line items — and the description explicitly separates itself from three siblings (get_action_usage, get_business_profile, get_financial_summary). However, there is no verb and the phrasing 'stub subscription ... the plan they pay stub for' is muddled enough that an agent may be unsure whether this returns a plan, a billing line-item list, or both.

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 names three concrete alternatives and the condition that selects each (actions used this period → get_action_usage; profile → get_business_profile; financials → get_financial_summary), which is real routing guidance. It stops short of stating when this tool itself is the right call (e.g. for reviewing plan tier or seat count), so it is clear context rather than a full when/when-not spec.

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