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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the safety profile is covered. The description adds a genuine data-boundary disclosure — 'Never exposes payment details' — plus the implicit scope that it targets only the authenticated user, which is useful context beyond the 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 sentences, front-loaded with what is returned and followed by when to use it; the field enumeration is long but each item earns its place by telling the agent what it can answer without a follow-up call. Slight density cost from the parenthetical billing-action list.

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 no output schema, the description carries the return-value burden and does so by enumerating the returned fields and listing the billing actions surfaced. Combined with the explicit usage triggers and the payment-data exclusion, an agent has everything needed to call it correctly.

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, so the baseline of 4 applies; there is nothing parameter-level for the description to clarify or miss.

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?

States a specific verb ('Show') and resource (the authenticated Nilyo user's account/subscription state), then enumerates the exact contents: login email, plan, trial/subscription status, limits, seats, members, and billing actions. It reads clearly against adjacent siblings like account_connection_status or list_connected_accounts but never names them, so differentiation is left to inference.

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?

Gives unusually rich trigger conditions: verifying which login the agent is connected to, user questions about plan/trial/price/seats/team, diagnosing a blocked action, or before proposing an upgrade. It stops short of naming alternative tools or stating when not to use it, which keeps it out of the top band.

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