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

Annotations already establish readOnly, idempotent, and non-destructive behavior, and the description reinforces this with 'Reads only; spends nothing.' It adds valuable behavioral context beyond the annotations by disclosing that a missing connection returns the setup link and that all account changes happen elsewhere. This is solid but not exhaustive; for example, it doesn't describe possible error formats, though the output schema may cover that.

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 three sentences with no filler: the first sentence front-loads what is reported, the second gives call timing guidance, and the third clarifies side effects and offloading. Every sentence contributes distinct value, and the key facts are immediately visible.

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 tool with annotations and an output schema present, the description is complete: it explains what the tool reports, when to call it, what happens on failure, and that it has no side effects. Nothing an agent needs to decide whether to invoke this tool is missing.

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 and the input schema is empty with 100% schema coverage, so there are no parameter semantics the description needs to add. With no parameters, the baseline is 4, and the description appropriately focuses on what the call returns instead of parameters.

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 ('Report') and a clear resource ('whether this session can buy'), then enumerates the exact outputs: connection status, payability, balance, per-call and daily limits, and used allowance. It is readily distinguishable from siblings like apiosk_execute or apiosk_compare, whose purposes are different operations rather than status reporting.

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 gives explicit when-to-use guidance: call it first in any conversation that might end in a paid API call, and again when a purchase is refused. It also tells the agent what not to do here (signing in, topping up, setting limits happen elsewhere), which prevents incorrect routing.

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