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

Annotations only declare readOnlyHint=false and destructiveHint=true; the description adds substantial behavioral context beyond them, including that it does not move money, that the invoice flips to paid when payments cover the total, that overpayment requires confirmOverpay, and that without confirm:true the call is a preview. This is exactly the mutation-safety detail the annotations cannot convey.

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?

Front-loads the core action, then layers scope, payment-application logic, and confirm semantics in tight sentences with zero filler. 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 destructive mutation with no output schema, the description covers the crucial points: what changes, the confirm gate, and the preview result with the balance. Return details for the success case are only lightly implied, but nothing critical to correct invocation is missing.

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 seven parameters, making 3 the baseline. The description adds only a small increment ('day... not in the future') and otherwise restates the amount, method options, and note that the schema already covers.

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 ('Records that the client paid... on a sent invoice') and immediately scopes it against payment-processing ('it does not charge or move money'). An agent can distinguish this from create_invoice, send_invoice, or a charge action without opening any schema.

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?

Clear context for recording full or partial payments, plus explicit conditions for confirm:true and confirmOverpay when over the balance. It does not name alternatives like remove_invoice_payment, but the when-to-use and preconditions are well established.

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