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

Annotations already give readOnlyHint=false, openWorldHint=true and destructiveHint=false, so the write/non-destructive profile is covered. The description goes beyond that by clarifying that the invoice balance actually decreases, that a fully paid invoice flips to paid, and notably that it 'moves no money and charges no card' plus the API-key and confirmation requirements.

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 first two sentences say essentially the same thing ('Record a ... payment received against an invoice' / 'Records a payment you received against one invoice'), which is redundant. The confirmation and API-key sentences earn their place, but the opening wastes space.

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 5-parameter mutation tool with no output schema and full schema coverage, the description supplies the missing behavioral context: what changes, that no money moves, and the confirmation/auth requirements. It is nearly complete; only the usage-vs-alternative angle is unaddressed.

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 five parameters (invoice_id, amount, method, date, reference). The description adds no syntax, format or examples beyond that, so the baseline 3 applies.

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 cash, check or other payment received against an invoice') and describes the effect on the invoice. An agent can distinguish this from yardbook_get_invoice, yardbook_list_invoices and the other Yardbook siblings without opening a 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?

The description says what the tool does and notes a per-call confirmation default, but never tells the agent when to prefer this over an alternative (e.g. an offline/manual payment path) or when it does not apply. Usage is only implied by the purpose statement.

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