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

Annotations provide no safety profile (all hints are false or minimal), so the description carries the burden. It discloses the state transition (stamps paid_at) and a key constraint (cannot be applied to void), but doesn't mention edge cases like applying to an already-paid invoice, error behavior, or side effects. Adequate but with gaps.

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?

Two sentences, front-loaded with the purpose, and includes the critical constraint and required parameter. No redundant 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?

For a one-parameter mutation tool, the description covers the core action and preconditions, but leaves out return behavior, error conditions, and how to obtain invoice_id. It is roughly minimum viable for an agent to attempt the call, but not complete enough to handle unexpected situations.

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 0%, so the description must explain invoice_id. It only restates that the field is required, which duplicates the schema, and gives no format, source, or meaning. It fails to compensate for the lack of schema documentation.

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?

Clearly states the action (mark invoice as paid), the resource (invoice), and the effect (stamps paid_at). It also differentiates from void_invoice by explicitly stating it cannot be applied to void invoices, making the tool's scope unambiguous.

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?

Provides clear context: it applies to draft or sent invoices and explicitly excludes void invoices. However, it does not name alternative tools (e.g., update_invoice, send_invoice) or explain when those would be preferred, so it stops short of full alternative guidance.

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