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

readOnlyHint already covers the safety profile. The description adds two pieces of real behavioral context beyond annotations: the call is free, and the result is scoped to "the key in use." It does not disclose auth failures, rate limits, or whether a missing/invalid key errors out.

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 fragments, front-loaded with the cost fact and then the payload. Nothing is wasted, though the telegraphic "Free." fragment reads as a label rather than a sentence and could carry slightly more structure.

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 does the job of listing what comes back (credit balance, plan, workspace). For a zero-parameter read tool this is nearly complete, missing only the detail of returned field shapes or the behavior when the key is invalid.

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 the schema imposes no semantic burden and the baseline of 4 applies. Nothing in the description is needed to explain parameter usage.

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 specific resource and the exact data returned: credit balance, plan, and workspace. It is unambiguous against siblings like list_models or get_image_status, though it never explicitly says it takes no parameters or why it exists as a distinct lookup.

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" implies the operation costs no credits, which is a lightweight usage signal (call it before expensive generation to check balance), but it never states when to call this versus other tools or what preconditions exist for the key in use.

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