Add a line to a customer's balance (write)

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

No annotations are present, so the description carries the burden. It discloses the operation type ('WRITE'), the effect (creates a line, no invoice), sign/currency semantics, and the behavioral caveat that the entry merely sits in balance until bill_customer runs. This is strong, though it does not cover reversibility, permissions, or failure behavior.

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?

Four short sentences, each earning its place: intent, sign/currency, non-invoicing caveat, and use case. Front-loaded with 'WRITE' and the primary action.

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 mutation tool with no annotations and no output schema, the description provides the key contextual frame: what the operation does, what it does not do, and the required ordering with bill_customer. It omits response/return details and prerequisites, but the input schema fully covers parameters; an agent is adequately equipped for selection and 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?

Schema coverage is 100%, so baseline is 3. The description adds segment currency context and reiterates sign meaning, but most parameter semantics (date/period exclusivity, ensure_billable, label) already exist in the schema. It does not substantially extend schema meaning.

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?

States a specific verb and resource: 'Creates a line in the balance of a ProAbono customer'. Clarifies debit/credit semantics and explicitly contrasts with bill_customer ('does not invoice'), distinguishing it from the closest sibling without opening schemas.

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?

Explicitly names the alternative: 'bill_customer is what turns the balance into an invoice' and states sequencing ('only useful in that order'). Provides a concrete use case ('one-off charge or a goodwill credit that the catalogue does not cover'), which functions as a when-to-use instruction.

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