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

Annotations already convey readOnly, idempotent, and non-destructive behavior. The description adds meaningful context: that the data is public, that it does not evaluate risk or create a trust receipt, and that it's safe to use in planning flows. No contradiction with annotations.

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: the first states purpose and scope, the second states suggested usage and an important non-goal. No filler or redundancy.

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 zero parameters and an output schema present, the description fully covers when to use it, what it covers, what it avoids, and its limitations. Nothing else an agent needs to know before calling it is missing.

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, so the description has no parameter-related burden. The baseline for zero parameters is 4; the description doesn't provide any parameter semantics because none exist and none are needed.

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 states a clear read-only intent and enumerates the exact domains covered (costs, trial availability, idempotency, top-up/payment paths). It also explicitly differentiates itself from siblings by stating it does not evaluate risk or create trust receipts.

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 gives an explicit 'when to use' trigger: before budgeting or onboarding. It also states what it does NOT do (risk evaluation, trust receipt creation), which encourages the agent to look elsewhere, but it doesn't name the alternative tools directly.

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