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

No annotations are provided, so the description carries the full burden. It does disclose two useful traits beyond the schema: the result is scoped to 'your API key' (auth context) and the call is 'Free' (no credit consumed). It does not describe return shape or whether the read is eventually consistent, but for a zero-arg read this is close to adequate.

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?

Two short sentences, zero filler, with the operation described first and the cost note second. Every clause earns its place.

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 parameterless read with no output schema, the description tells the agent what it gets (a credit balance), whose balance (the API key's), and the cost. Little more is needed; only the return format is left unstated, which is low stakes here.

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 no parameters, so the schema has nothing to document and there is no semantic gap to fill. Baseline for a 0-param tool is 4.

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 ('Show the remaining credit balance') scoped to the caller's API key. It points away from sibling buy_credits and list_credit_packs by nature of being a read, but never explicitly distinguishes itself from them.

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 by the resource itself: you call it when you need to know your balance. The 'Free' tag hints that cost is not a barrier, but there is no explicit when-to-use or when-not-to-use guidance relative to alternatives.

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