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

Annotations already establish that this is a read-only, idempotent, non-destructive, closed-world operation. The description adds useful negative scope by ruling out prices, catalogue data, and upgrade offers, which prevents the agent from expecting commercial information. It does not discuss auth or rate limits, but those are less critical for a zero-argument read tool.

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?

Three sentences, all front-loaded and earning their place: the first states what is returned, the second states when to use it, and the third prevents misalignment about what is not included.

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 tool with no output schema, the description does everything needed: it identifies the returned fields, the user intent that triggers it, and the boundaries of its scope. Nothing essential 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, which sets the baseline at 4. The description reinforces this by stating it takes no arguments, and there are no parameters whose meaning needs further explanation.

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 uses a specific verb-plus-resource formulation: it returns the caller's credit balance, plan tier, and paid-feature unlock status. That is distinct from every sibling tool, which all operate on jobs, documents, applications, or profiles.

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?

It gives an explicit trigger condition: use it when the user asks about remaining credits or their current plan. The negative scope (no prices, no plan catalogue, no upgrade offer) further clarifies when the tool is not appropriate, though no alternative tool is named for those adjacent needs.

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