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

With no annotations, the description carries the behavioral transparency burden. It discloses that the output is aggregated by calendar month and spans all categories, but it does not describe return format, date coverage, or whether this is a pure read operation. This is adequate for a zero-parameter query but not richly transparent.

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?

A single sentence that is efficient and front-loaded. It loses a point because 'Calendar-month' duplicates 'monthly' from the title and 'credit spend' is repeated, though the 'across all categories' addition earns its place.

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, no-output-schema tool, the description is nearly sufficient: it names the aggregation period and scope. It does not spell out the exact return values or whether the data covers a specific range, but the simplicity of invocation lowers the burden.

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 no parameters, so the baseline is 4. The description correctly does not invent parameter details, and there is nothing beyond the empty schema to document.

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 clear resource and aggregation: a calendar-month breakdown of credit spend across all categories. It goes beyond the title by specifying the 'across all categories' scope, which helps distinguish it from per-agent or per-type credit usage tools. It lacks an explicit verb but the intent 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?

The description gives no guidance on when to prefer this tool over sibling credit tools such as get_credit_usage_by_type or get_credit_usage_by_agent. It implies a monthly reporting use case but does not state exclusions or alternatives.

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