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

Annotations only declare readOnlyHint=false and destructiveHint=false; the description goes further by disclosing the resulting status transitions (PAID vs PARTIAL), the defaulting behavior, the absence of fiscal computation, and the returned values. It does not mention the double-payment rejection surfaced only in the referencia_pago schema field, so it misses one meaningful behavioral guard.

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?

Four short sentences, front-loaded with the action and its precondition, then defaults, then side effects, then return shape. No filler and no repeated information.

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?

No output schema exists, and the description compensates by naming the return fields (new status, paid, outstanding, payment id). It covers the essential call contract for a low-risk mutation, but omits error/idempotency behavior for a tool that can record money twice.

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?

With 50% schema coverage, the description partially compensates by restating the amount and date defaults, but it adds nothing about method, notes, or the uniqueness semantics of referencia_pago. Of the six parameters, only one required field is implied by context; the description mostly repeats what the schema already says.

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 against a finalized invoice') and adds a scoping constraint that separates it from siblings like list_payments or cancel_invoice. An agent can tell exactly what this tool does and to what object 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?

The 'against a finalized invoice' precondition tells the agent when this tool applies versus create_invoice/finalize_invoice, and 'No fiscal logic, it records what the user says was collected' sets the expectation that it won't compute taxes. There is no explicit exclusion (e.g. what to do for unfinalized invoices) or named alternative, so it falls short of a 5.

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