get_billing_info

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

Annotations already indicate readOnlyHint=true, so the baseline safety is known. The description adds behavioral context by clarifying the content scope (tier limits, overage rates, per-operation costs) and that it does not cover credit balance. This goes beyond annotations and prevents misuse, though it stops short of describing output structure or edge cases.

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 with no filler. The first sentence front-loads what is returned, and the second gives usage context and alternatives. Every clause earns its place.

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 zero-parameter read-only tool with an output schema present, the description fully covers purpose and usage context. It tells the agent exactly when to call it and clarifies what it does not do, making it complete for selection and invocation.

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 has zero parameters and the schema properties are empty, so the baseline is 4. The description correctly implies no parameters are needed; no additional parameter semantics are required.

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 description clearly states the tool provides subscription plan details including tier limits, overage rates, and per-operation costs. It uses a specific resource ('subscription plan') and immediate content list, and distinguishes from siblings by explicitly noting it is not for credit balance, which points to get_credits/whoami.

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 explicitly tells when to use: 'before running expensive operations' and provides exclusions and alternatives: 'not for credit balance — use whoami or get_credits'. This is direct when/when-not guidance with named alternatives.

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