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

With no annotations provided, the description carries the full burden of behavioral disclosure. It reveals the default source and excludes invoices, but does not explicitly state that this is a read-only operation, describe the response format, or mention any side effects, errors, or prerequisites. The 'get' in the name implies read, but that's not explicit.

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 extremely concise, using only two clauses to convey the core purpose and a key exclusion. It is front-loaded with the primary function and contains no redundant or filler content, making it efficient and easy to parse.

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 read tool with no output schema, the description is incomplete. It does not describe what the returned billing setup contains, how the 'live' source differs in output, or what errors might occur. It also lacks guidance on when to use 'live' versus 'ledger', which is critical for effective invocation.

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 input schema covers both parameters with descriptions (customer_id and source with enum and default). The description adds no new meaning beyond restating that the default is the ledger, which is already in the schema. With 100% schema coverage, the baseline is 3, and the description provides no additional parameter value.

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 retrieves billing setup for a single customer, with the default source being the ledger, and explicitly excludes invoice retrieval. This distinguishes it from invoice-related operations, though it doesn't specify what 'billing setup' includes or differentiate it from sibling tools.

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?

No explicit guidance on when to use this tool versus alternatives. The only usage hint is the negative statement about not retrieving invoices, which is more of a limitation than a positive directive. It doesn't explain when to choose 'ledger' vs 'live' sources either.

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