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

The readOnlyHint annotation already establishes this as a safe read operation, so the description need not belabor that. It adds the 'GET /balance' endpoint and the concept of a 'configured' account, but it does not disclose output format, units, or potential error conditions; these are minor given the simplicity and annotation coverage.

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 two short sentences with no filler, front-loads the core purpose, and includes a useful API reference. Every word contributes essential meaning.

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, read-only tool, the description is nearly complete: it names the return concept (remaining balance/usage) and the underlying endpoint. It does not specify format, currency, or units, but these are not critical for invoking the tool correctly and no output schema is present to fill the gap.

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, so the schema fully covers input requirements and the description need not add parameter detail. The description's mention of a 'configured account' clarifies that no account identifier needs to be supplied, which is useful context beyond the empty schema.

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 clearly states the action ('Return the remaining balance / usage') and the resource ('configured Api2Pdf account'), and it is unmistakably distinct from the sibling tools, which all perform conversion, compression, merging, or file operations. The specific endpoint reference also reinforces the tool's scope.

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 usage context is implied rather than explicit: an agent can infer this tool is for checking account credit/usage, and no alternative or exclusion criteria are mentioned. While the role is clear given the sibling list, the description does not state when to prefer this over, for example, api2pdf_get_status, which also queries account/job information.

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