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

With no annotations provided, the description carries the full disclosure burden. It usefully states this call is "Free" (no credit consumed) and implies read-only access scoped to "your API key", but says nothing about authentication requirements, rate limits, or behavior on an exhausted/invalid key — a notable gap for a billing-adjacent endpoint.

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 clauses with zero filler, front-loading the primary return value (remaining credit) before the secondary one (prices). Nothing is padded or repeated from the title.

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-parameter, no-output-schema tool, the description adequately covers what comes back at a high level. It is slightly thin on the nature/format of "current prices" and on failure modes, but an agent has enough to call it correctly.

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, so there is nothing for the description to disambiguate; baseline 4 applies. The description correctly declines to invent any input requirements.

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 names the concrete resource returned (remaining credit for the API key) plus a secondary output (current prices), so an agent knows exactly what this call yields. It does not, however, differentiate itself from the nearby onyx_payment_info sibling, which the agent may conflate with billing/credit queries.

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?

There is no statement of when to call this versus onyx_payment_info or the other siblings, and no prerequisites or sequencing guidance. The word "Free" implies cost-free invocation but is not framed as usage guidance.

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