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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false. The description adds useful context beyond annotations: the operation is stateless and in-memory, it returns a new synthesized document rather than mutating server records, and it produces PDF output. It does not discuss authentication or limits, but those are less critical here.

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 description is two sentences and front-loads the core behavior. The example is compact, though using an empty document object as the example payload is slightly confusing since document is a required object containing invoice data.

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?

Given that an output schema exists and annotations cover safety traits, the description provides enough context for an agent to understand that this is a stateless, non-mutating synthesis operation. It could be improved with explicit sibling differentiation, but the essential behavioral picture is complete.

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 parameters including defaults for amount_paid. The description adds only a minimal example call and does not explain parameter interactions or formatting beyond what the schema provides, making the baseline 3 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?

The description states a specific verb and resource: stateless in-memory payment calculation and PDF synthesis returning a Receipt or partial-payment Invoice. It clearly distinguishes itself from mutating tools by emphasizing 'without mutating server records,' though it does not explicitly contrast itself with siblings like calculate_totals or generate_document.

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 implies usage when a stateless payment receipt or balance calculation is needed, but it never states when to choose this over calculate_totals or generate_document. It provides an example call but no explicit conditions or alternatives.

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