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

The description clearly describes a write operation ('Record a payment', 'generate an official Receipt'), yet annotations declare readOnlyHint=true. That is a direct contradiction about whether the tool mutates state, and it is the single most important behavioral fact for the caller.

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?

One well-formed sentence with the action front-loaded and no redundant restatement of the name. Mild promotional padding ('instantly', 'official') costs it a point but does not obscure meaning.

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?

An output schema exists, so return values need not be explained. However, for a mutation with a nested 'document' payload, the description omits prerequisites (invoice must already exist), overpayment handling, and whether the source document is modified in place — and the readOnly annotation actively misleads.

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% and each parameter already explains itself, including the amount_paid default behavior. The description adds only 'remaining balance tracking' and does not supplement anything the schema lacks, so 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+resource ('Record a full or partial payment against an invoice') plus the outcome (receipt or updated invoice). It is distinguishable from siblings like preview_document and generate_document, though it never names them explicitly to sharpen the boundary.

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 full-vs-partial distinction is described, which implies when to use it, but there is no explicit when-not guidance and no reference to alternatives such as preview_document or calculate_totals. An agent must infer the routing.

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