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

Annotations already declare readOnlyHint=true and destructiveHint=false. The description reinforces this by stating it only checks a balance, and adds the useful context that the balance is tied to the API key. No side effects, auth requirements, or rate-limit concerns need to be disclosed for this read-only operation.

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?

The description is a single, direct sentence with no filler. It front-loads the action and resource, making it immediately scannable and useful for an agent.

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?

This is a minimal, zero-parameter read-only tool with an output schema and annotations already covering safety. The description fully states what the tool does, and there are no missing prerequisites, side effects, or alternative routing concerns that an agent would need.

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 accepts zero parameters, so there is no parameter semantic burden on the description. The schema fully covers the empty parameter set, and the description appropriately focuses on the result rather than inputs.

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 ('Check') and clearly identifies the resource ('remaining credit balance for your API key'). It is unambiguous and distinct from sibling tools, which focus on data retrieval, funding signals, or catalog searches rather than 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 description makes clear that this tool is for checking the credit balance associated with the caller's API key. No explicit alternative is named, but the context is self-evident and the tool's zero-parameter nature reduces ambiguity about when to use it.

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