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

With no annotations, the description carries the full burden of behavioral disclosure, and it does disclose that this is a cost-free read of the caller's own balance. However, it does not address whether authentication is required, how the balance is represented, or what the response looks like.

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?

This one short sentence contains no wasted words, and it leads with the essential information: what is fetched and whose balance it is. The parenthetical about cost is a compact addition.

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 no-parameter read that returns a single value and has no output schema, the description covers what an agent needs in order to decide to call it. The remaining gaps, namely the balance representation and the authentication model, are minor.

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 has zero parameters, so there is no parameter semantics to explain; a baseline of 4 applies. The description correctly implies that no input is needed.

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 and resource: checking the caller's own credits balance. This is unambiguous and clearly distinct from every sibling tool (domain_timeline, ledger_pulse, stripe_leaderboard, etc.), none of which report account balance.

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 '(免费)' note implies that calling the tool is free, which encourages its use, but the description gives no explicit condition for using it and no alternative tool to use instead. Usage is implied rather than guided.

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