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

Annotations already cover readOnly, idempotent, non-destructive and closed-world, so the bar is lower; the description still adds two valuable facts beyond them — that the call itself is free and that the connection may be prohibited from spending credits at all. It doesn't say what happens when credits are exhausted or how the limit resets.

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?

It is short and front-loads the most decision-relevant word ('Free.') before listing the four returned facts. The list is a sentence fragment with a slightly awkward switch between 'The person's credit balance' and 'whether this connection', but no sentence is wasted.

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?

With no output schema, the description carries the burden of describing return values and does so by naming all four. Minor gaps remain — units or currency of the balance, and what the limit window means — but an agent can call it correctly and interpret the result well enough.

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 spends its words on return content instead.

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 enumerates exactly what the tool returns: credit balance, per-picture cost, remaining daily app limit, and whether the connection may spend credits. That is specific enough to separate it from siblings like make_character_picture, which consumes credits, though it never states the verb 'check/retrieve' outright.

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?

'Free' signals there is no cost to calling it, and the per-picture cost output implies it should be consulted before image-generation tools, but the description never explicitly says when to call it or when not to. Usage is implied rather than stated.

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