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

Annotations already establish the safety profile (readOnlyHint, idempotentHint, destructiveHint=false, openWorldHint=false), so the bar is lower. The description nonetheless adds real domain behavior beyond the annotations: ordering (newest first), the meaning of the `current` marker, and the non-obvious rule that history restarts after cancellation when the free plan opens a new subscription. It omits any note on pagination or result size limits.

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?

Effectively two sentences, front-loaded with the core purpose before the clarifying detail. The only waste is that the first line repeats the title verbatim, which buys the agent nothing. The 'history starts again after a cancellation' sentence earns its place by explaining a surprising data shape.

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-argument, read-only listing tool with no output schema, the description is nearly sufficient: it characterizes the records, their order, and the `current` marker so the agent can interpret results without a schema. The missing pieces are pagination behavior and any contrast with get_usage, which is the one thing an agent most needs in this sibling set.

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 there is nothing for the description to disambiguate and the baseline of 4 applies. The schema is empty with additionalProperties=false, matching the description's implication that all filtering is implicit.

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+resource ('List usage by billing period') and enriches it with scope details: every billing period of the current subscription, newest first, with messages used against each period's limits. It is clear what the tool returns, but it never distinguishes itself from the sibling get_usage, leaving the agent to guess which usage tool to pick.

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: it is a historical listing of billing periods, so an agent can infer it is for time-series/billing-period inspection. There is no explicit when-to-use, no exclusions, and critically no guidance on when to prefer this over the sibling get_usage, so the routing decision is left to inference.

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