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

Annotations already cover read-only, idempotent, non-destructive behavior, so the bar is lower. The description still adds substantive context: no-card trials report 25 lifetime minutes with zero price and no overage, paid plans report the mapped subscription price and current billing-cycle usage, and unavailable billing data returns an error rather than a partial result. It does not describe auth or scoping requirements for 'accessible businesses'.

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?

The core scope is front-loaded in the first sentence and every later sentence adds a distinct rule (trial vs paid reporting, raw vs weighted call count, extra lines, the activation caveat, error behavior). It is dense and slightly run-on, but nothing is redundant.

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 no-parameter read with an output schema, the description covers the interpretive traps an agent would otherwise hit: which call count counts against allowance, that extra purchased lines are included, and that missing billing data produces an error. The only gap is how the business/account is scoped given no parameters, which the agent must infer from context.

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, which is the baseline-4 case. The description appropriately spends its space on interpreting the returned fields instead of on arguments.

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 first sentence gives a specific verb and resource: 'Get plan terms and usage for accessible businesses.' It clearly frames the tool as a billing/plan read rather than a status or config read, distinguishing it from siblings like get_checkout_status or get_billing_contacts. It stops short of naming a sibling or an explicit boundary, so it falls just below the top band.

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: the tool answers billing/allowance questions, and the caveat 'A balance does not prove activation or inbound routing' implicitly routes activation questions elsewhere. No alternative tool is named and no explicit when-not-to-use statement is given, so an agent must infer the boundary from sibling names.

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