cost_report

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

With no annotations provided, the description carries the full burden of disclosing behavior. It states the tool returns total spend and lines changed, implying a read-only aggregation, but does not explicitly confirm it is non-destructive or describe any side effects. It also does not mention any limitations or prerequisites beyond the root parameter.

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 short and front-loaded with the core purpose, followed by a clear Args section. Every sentence adds value and there is no redundant 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?

The description covers the purpose, parameter semantics, and the output metrics. Since an output schema is provided, the description does not need to detail the return structure. However, it lacks explicit usage guidance or prerequisites, which would make it more complete.

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 description explains the single parameter 'root' as a directory to search, and specifies its default to the standard transcript location. This adds meaning beyond the schema, which only defines the type and default null. The description fully compensates for the 0% schema coverage.

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 tool aggregates cost across sessions under a root and lists the specific metrics returned (total spend, total lines changed, spend per 100 lines changed). This distinguishes it from sibling tools like list_sessions and analyze_session, which serve different purposes.

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 does not explicitly state when to use this tool versus alternatives like analyze_session or list_sessions. The purpose is clear but there is no guidance on exclusions or conditions that would make a different tool more appropriate. This is implied rather than explicit.

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