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

Annotations already declare openWorldHint=false and destructiveHint=false, but the description adds the genuinely non-obvious fact that marking paid does not charge the customer or call a payment provider — the key question for an agent about a write on money. It leaves gaps on repeat-call behavior, reversibility, and error conditions for already-paid invoices.

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 short sentences, front-loaded with the action and its precondition, then a negative constraint. No filler, and each sentence adds information an agent needs.

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?

With an output schema present and annotations covering the safety profile, the description only needs the precondition and external-side-effect picture, both of which it supplies. Remaining omissions — idempotency behavior and what happens on retry — are modest but real for a three-required-parameter mutation tool with no schema docs.

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 all three parameters (invoiceId, idempotencyKey, confirmationToken) rely on the description for meaning. The text gestures at invoice identity and the one-use confirmation but never explains the confirmationToken's provenance or the role of idempotencyKey, leaving the most failure-prone parameter undocumented.

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 specific verb-plus-resource ('Marks the exact prepared invoice as paid') and scopes it to a prepared invoice, which implicitly separates it from prepare_invoice_payment_record. It stops short of naming the sibling or the two-step flow explicitly, so the differentiation is inferable rather than stated.

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?

'Only after an explicit, one-use confirmation' communicates the precondition for calling, and 'the exact prepared invoice' signals that a preparation step must precede it. It does not name the preparing tool or say what to do if no prepared record exists, so routing is clear in context but not fully spelled out.

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