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

No annotations are provided, so the description carries the full burden. It signals a read operation via 'check' and explains the unit semantics (1 credit = US$0.0001), but says nothing about auth requirements (the Bearer option lives only in the schema), behavior for an invalid or missing account_key, or what the response looks like.

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, the core purpose leading and the unit conversion following as a compact interpretation aid. Nothing is wasted and nothing important is buried.

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 single-parameter read tool with no output schema, the description should at least characterize the returned value. It conveys the quantity (remaining credits) and its unit but not the response shape or failure behavior, leaving a modest gap for an unannotated tool.

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?

Schema coverage is 100% and the single account_key parameter is fully documented there, including the Authorization: Bearer alternative. The description adds no parameter-level detail, so the baseline of 3 applies.

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 states a specific verb and resource ('Check how many credits an account has left'), so an agent immediately knows this is a balance read. It doesn't name or contrast with siblings like pricing or deposit_status, but no sibling actually overlaps with this capability, so the purpose is unambiguous.

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?

Usage is only implied by the verb 'check'; there is no statement of when to call this versus pricing (which presumably returns rates) or deposit_status. The credit-to-dollar conversion gives useful interpretation context but is not guidance on tool selection.

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