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

Beyond the annotations (readOnly=false, destructive=false, openWorld=true), the description discloses the amount cap against remaining balance, the date-required condition, the resulting invoice state ('paid or partly paid'), the default confirmation behavior, the note that it reaches other people, and the API key requirement. That is substantive behavioral context an agent needs before mutating data.

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-loaded with the core action, then scoping and constraints, then the confirmation/auth caveats. One minor redundancy: 'By default you confirm each call; you can switch that off for this tool' is effectively repeated by 'Reaches other people: confirm with the user before each call.'

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 output schema, it covers the key gaps: what changes (invoice marked paid/partly paid), limits on input, confirmation default, and auth. It does not describe failure modes (e.g. overpayment rejection response) or idempotency, but nothing essential 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 three parameters, including the amount cap and the date requirement. The description largely restates those same semantics rather than adding new detail (e.g. date format or precedence when the invoice is not foreign-currency). Baseline 3 is appropriate.

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 — 'Record a payment received on an invoice' — and immediately narrows scope to 'one invoice', which separates it from list/get invoice siblings. An agent knows exactly what this tool does without opening the 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?

Gives concrete usage conditions: the date is required for foreign-currency or cash-method invoices, and the amount cannot exceed the outstanding balance. It doesn't name an in-app alternative (e.g. a bulk or batch payment tool), but the conditions for correct invocation are clear.

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