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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is clear. The description adds valuable behavioral context: it reveals that the tool returns available billing actions (subscribe, upgrade, add seats, invite) and explicitly states it never exposes payment details. This goes beyond the annotations and helps the agent set user expectations.

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 description is two sentences, front-loads the core purpose, and every clause earns its place. The usage triggers are listed compactly, and the payment-details exclusion is a single short sentence. No redundancy with the schema or annotations.

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 strong annotations, the description is complete. It tells the agent what data is returned, when to use it, and what it will not return. There is no output schema, but the description enumerates the return contents well enough for an agent to decide whether to call it.

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 there is no schema burden. The description compensates by explaining what the tool returns (plan, trial status, limits, seats, members, billing actions), which is the closest thing to parameter semantics for a parameterless tool. A baseline of 4 is appropriate for zero-parameter tools.

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 specific verb ('Show') and resource ('the user's Nilyo plan, trial/subscription status, account limits, team seats and members, plus the available billing actions'). It clearly distinguishes this from sibling tools like account_start_subscription and account_change_plan by focusing on read-only display of subscription state and available actions, not performing them.

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?

The description explicitly lists when to use this tool: 'when the user asks about their plan, trial, price, seats, team, why an action is blocked, or before proposing an upgrade.' It also provides a negative constraint ('Never exposes payment details'), which helps the agent avoid using it for payment-sensitive queries. This is strong usage guidance.

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