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

The annotations already indicate a write operation (readOnlyHint=false), and the description adds a meaningful side-effect: optionally writing the cash row when account_id is provided. It does not contradict the annotations and provides behavioral context beyond the structured fields.

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 two tight sentences with no filler. It front-loads the core purpose and then adds the important side-effect in the second sentence. Every phrase contributes meaning.

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 six-parameter record operation with zero schema description coverage, the description covers the core behavior but leaves some parameter semantics (date, note) and potential effects on the loan balance unexplained. The output schema and annotations reduce some burden, but the description alone is not fully complete for all inputs.

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 description coverage is 0%, so the description must compensate. It clarifies the meaning of 'kind' (instalment vs prepayment) and 'account_id' (moved through the bank account, writes cash row), while 'loan_id' and 'amount' are largely inferable from names. However, 'date' and 'note' receive no semantic explanation.

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 states a specific action ('record') on a clear resource ('loan payment') and indicates two kinds of payments (instalment/prepayment) plus the lending direction. It does not explicitly contrast with siblings like add_loan, update_loan, or log_transaction, but the operation is specific enough to be identifiable.

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 gives useful guidance for when to include the optional bank account ('which also writes the cash row'), but it does not say when to use this tool versus alternatives such as create_transfer or log_transaction. No exclusions or explicit routing to sibling tools are provided.

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