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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so the safety profile is covered. The description adds a genuine behavioral fact not in structured data: the call is free, meaning it does not consume the credits it reports on — a meaningful signal in a toolset that otherwise bills credits.

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, front-loaded with what is shown and closed with the cost note. The enumeration of returned fields is long but every item earns its place since there is no output schema to carry them.

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 full burden of describing the return payload and does so precisely, listing all six pieces of information. Annotations cover the safety profile and no parameters need explaining, so nothing an agent needs to invoke and interpret this tool 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 takes zero parameters, so the baseline is 4. There is nothing for the description to disambiguate, and nothing misleading about the empty schema.

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 (shows) tied to a specific resource (the signed-in account) and enumerates exactly what is surfaced: credits left, granted, spent, expiry, plan, and admission status. None of the sibling tools touch account state, so it is trivially distinguishable from the film/file/job operations around it.

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 implied rather than stated: an agent can infer this is the tool for checking remaining credits or plan before or after consuming a paid operation. There is no explicit when-to-use or when-not-to-use guidance, nor any mention of prerequisites, though the absence of alternatives for account state limits the practical gap.

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