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

Annotations already indicate readOnlyHint=false, destructiveHint=false, idempotentHint=false, so the agent knows this is a mutating, non-idempotent operation. The description adds important behavioral context: the amount defaults to the suggested settle-up amount from get_expenses, and it emphasizes 'Only after the money was actually sent,' which is a critical precondition. This goes beyond the annotations and helps the agent avoid premature calls.

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 sentences with no wasted words. The core action is front-loaded, the default behavior is stated, and the critical precondition ('Only after the money was actually sent') is included. Every sentence earns its place.

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 mutating tool with no output schema, the description covers the essential context: what the tool does, the default amount behavior, and the precondition. It doesn't describe the return value or what happens after recording, but given the simplicity of the operation and the full schema coverage, this is adequate. The only minor gap is not explaining what the response contains, but that's not critical for invoking the tool correctly.

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 100%, so the schema already documents all parameters. The description adds the key semantic that 'amount' defaults to the suggested settle-up amount, which is valuable. However, it doesn't add much beyond that for the other parameters, which are already well-described in the schema. Baseline 3 is appropriate given full schema coverage.

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 action: recording that the person you act for paid someone back (settling up). It specifies the resource (payment) and the context (settling up a debt), and distinguishes it from expense-related tools by focusing on repayment. The verb 'record' plus the object 'payment' is specific and unambiguous.

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 clear context: use this when money was actually sent to settle up. It also mentions the default amount behavior tied to get_expenses, which implies when to use it (after checking expenses). However, it doesn't explicitly state when not to use it or name alternatives like add_expense, though the settling-up framing makes the distinction fairly clear.

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