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

Annotations already declare readOnlyHint and idempotentHint, so safety is covered by structured data. What the description adds beyond that is genuinely useful: it enumerates the returned fields (plan, used minutes, remaining prepaid minutes, expiry) in the absence of any output schema. It does not mention auth scope or billing-cycle edge cases, but for a trivial read tool this is close to sufficient.

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?

A single sentence with no filler that front-loads the resource ('the plan') and then the specific quantities returned. Nothing could be cut without losing information the agent needs.

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 no output schema, the description supplies precisely the missing piece: what data the call returns. 'This billing period' also scopes the reporting window, which the agent cannot infer elsewhere.

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 schema-level parameter semantics are not a concern and the baseline of 4 applies. There is no parameter format or default that the description needs to compensate for.

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 enumerates exactly what resource is reported: plan, plan minutes used this billing period, prepaid minutes left, and their expiry. Against siblings that are all transcription actions, this account/billing scope is unmistakably distinct, so an agent can select it without opening the schema.

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 implies the use case (checking quota/remaining minutes and expiry) but gives no explicit when-to-use statement, prerequisites, or named alternatives. A 'call this before transcribe_audio to verify minutes remain' style hint is absent, so guidance is inferable rather than stated.

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