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

The annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is fully covered. The description contributes one genuinely new behavioral fact — the call is free, i.e. it does not consume credits — but says nothing about what happens on an exhausted or invalid token, nor about the shape of the returned figures.

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 sentences with zero filler, and the core resource (remaining credits) is front-loaded before the secondary detail about paid models. Nothing could be cut without losing information.

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 no-parameter, read-only status tool with annotations covering its safety profile, the description does roughly the right amount. The one soft gap is that with no output schema, it could spell out the return fields (e.g. numeric balance, model count) more concretely.

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 schema itself is trivially complete.

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 gives a specific verb ('Show') and names the resource precisely: 'credits left on the access token' plus a count of already-paid models. That is enough for an agent to know exactly what data comes back, though the second clause ('how many models are already paid for') is slightly ambiguous about whether it is a count or a listing.

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' implicitly tells an agent this call costs no credits, which weakly encourages pre-flight checking, but there is no explicit statement of when to call it versus the other tools, no prerequisites, and no conditions under which it should be skipped. Nothing in the text routes the agent among the siblings.

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