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

No annotations provided, so description carries full burden. Discloses key behavioral traits: operation is read-only (no token spending) and works at zero balance. Could mention rate limits or response format, but for a simple balance check this is sufficient.

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?

Extremely concise: two sentences that front-load the core verb and resource. Every word adds value—no filler or redundancy.

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?

Covers the essential aspects: purpose, side effects, prerequisites. Lacks specification of the return value format, but given the low complexity (no params, no output schema), the description is mostly complete. A slightly richer description could mention the response type.

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?

Input schema has zero parameters, and schema description coverage is 100%. The description adds context by explaining that no input is needed and that the tool checks the balance of the authenticated key. Since there are no parameters, the description effectively fulfills the role.

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?

Clearly states the action ('Check the token balance'), the resource ('of the API key in use'), and a key property ('without spending any tokens, works even at a zero balance'). Distinguishes from sibling tools which are unrelated to token 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?

Explicitly describes when to use (to check token balance) and a prerequisite (Requires Authorization bearer key). No alternatives among siblings, so exclusion guidance is not needed. Could be more specific about typical use cases.

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