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

With no annotations, the description carries the full burden and does well: it discloses that a partial payment reduces the outstanding chased amount, that a covering payment closes the invoice and frees the free-tier slot, and that the return value is the outstanding amount. It omits permissions, idempotency/duplicate handling, and which currency the minor units belong to.

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?

A single front-loaded sentence leads with the action and then packs the two key consequences efficiently. The domain shorthand ('closes the ladder', 'frees the free-tier slot') is slightly jargon-heavy but still parses without prior context.

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 annotations and no output schema, the description covers the essential state change and the return value ('outstanding amount'). It is nearly complete, missing only permission requirements, idempotency behavior, and overpayment handling.

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 all four parameters are already documented, making 3 the baseline. The description adds only the semantic effect of amount_minor (partial vs. covering payment) and repeats the 'whole MINOR units' convention already in the schema; date, note, and invoice semantics are left entirely to the schema.

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 gives a precise verb+resource ('Record money received against a chased invoice') and specifies the unit convention, so the operation is unambiguous. It stops short of contrasting itself with siblings such as invoice_register or invoice_status, so it does not reach the sibling-differentiation bar for a 5.

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?

Usage is only implied by the phrase 'against a chased invoice' – the agent can infer this applies when money arrives for an outstanding chased invoice, but there is no explicit when-to-use, when-not, or named alternative. No guidance is given on duplicate payments or what happens if the amount exceeds the balance.

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