billing_get_funding_source

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

With no annotations, the description carries the full burden of behavioral disclosure. It explicitly states 'Returns metadata only — no sensitive details (card numbers, etc.)', which is valuable context beyond what the name or schema conveys, informing the agent that this is a read-only tool with limitations on output content. It does not disclose error handling or authentication requirements, but for a simple getter this is reasonable.

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 concise and well-structured, consisting of two short sentences. The first sentence states the primary purpose, and the second adds a clear limitation. Every word earns its place, with no redundancy or ambiguity.

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 simple tool with one parameter, no annotations, and no output schema, the description is reasonably complete. It tells the agent what the tool does and what it returns (metadata only), which is sufficient for selection and invocation. It does not describe the exact return structure or error scenarios, but the low complexity makes this acceptable.

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 only parameter, account_id, is not described beyond the schema's terse 'Account Id'. The description references 'an ad account', which implicitly ties the parameter to that entity, but it does not explicitly explain the parameter's meaning or format. With schema description coverage at 0%, the description does not fully compensate, though the single parameter is straightforward.

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's function: 'Get info about the configured funding source on an ad account.' It uses a specific verb ('Get') and identifies the resource ('configured funding source on an ad account'), which effectively distinguishes it from sibling billing tools like billing_get_invoice or billing_get_account_spend.

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 provides a clear context (retrieving funding source info for an ad account) but offers no explicit guidance on when to use this tool versus alternatives, and it does not mention exclusions or prerequisites. Since it's a simple getter, usage is implied rather than explicitly stated.

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