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

The annotations already establish read-only, idempotent, and non-destructive behavior. The description adds non-obvious behavior not covered by annotations: drafts are separated from finalized documents und currencies are never added together. The 'Free.' note also contributes context, though it is somewhat ambiguous.

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 compact and front-loaded: it states the verb, the resource, and the exact output contents in one tight sentence. 'Free.' is terse and communicates an additional trait without wasting space.

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 parameters and no output schema, the description carries the full burden of explaining what the tool returns—and it does: document counts by status, sold value per currency, and the rule that currencies are never summed. That is complete for a no-argument read-only call.

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 schema has zero parameters, so the description cannot add parameter-level meaning—it has nothing to clarify. The 0-parameter baseline of 4 applies, and no parameter information is missing.

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 resource ('the book') and enumerates exact outputs: counts of drafts and finalized documents, and total sold value per currency with drafts separate. This makes the tool clearly distinct from siblings like sale_get and sale_list, which operate on individual records.

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 aggregate-summary intent is unmistakable from the described outputs, so an agent can tell when to select this over per-sale tools. It does not explicitly name alternatives, but the distinction between summarization and individual-record access is contextually clear without exclusions.

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