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

The description correctly indicates a non-read-only action, but contradicts the annotation by claiming 'Idempotent' while idempotentHint is false. This is a serious inconsistency, so the score is 1.

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 concise sentences, front-loaded with the action, then usage context and a claim. No wasted words, efficient and clear.

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 simple state-transition tool with one parameter and an output schema, the description is largely adequate. However, the idempotency claim contradicts annotations and it doesn't address what happens if the invoice isn't in DRAFT state, leaving some gaps.

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?

The schema fully documents the single parameter (invoiceId) with 100% coverage, so the baseline is 3. The description adds no additional semantic meaning beyond the schema, which is acceptable for such a simple parameter.

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 as sent), the resource (invoice), and the state transition (DRAFT → OPEN). This distinguishes it from sibling tools like record_invoice_payment or void_invoice.

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?

Explicitly instructs to use after delivering the invoice via email or share link, providing clear timing context. Though alternatives aren't named, the 'Use after...' guidance effectively differentiates it from other invoice actions.

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