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

Annotations already declare readOnlyHint=true and destructiveHint=false, so safety is covered; the description adds non-obvious context beyond that: the invoice is the authoritative source over job status, the Paid In Full status is manually applied, and an API key with app access is required. It does not describe pagination or result-size behavior.

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?

Five compact sentences that each carry information (fields, source of truth, paid-flag workaround, sibling linkage, auth requirement). Slightly back-loaded on the core verb, which lands in the second sentence after the field list, but nothing is wasted.

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 no output schema, the description appropriately enumerates the returned fields, and it covers auth requirements and the invoice-vs-job-status behavior for a read-only list tool. Only pagination/default behavior is left to the schema, which is acceptable.

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 'from', 'page', and 'paid' are already documented with types and defaults. The description's mention of the paid flag is really usage rationale (why prefer it over job status) rather than parameter syntax or format detail, so it sits at the baseline for fully-covered schemas.

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 and resource ('Lists invoices') and enumerates the returned fields (number, customer, total, date, paid flag, pay-online link), so the agent knows exactly what it gets. It also distinguishes the source of truth ('read from the invoice itself rather than from the job status'), which differentiates it from job-oriented siblings.

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?

Gives actionable when-to guidance: use the paid flag instead of the Paid In Full job status, and notes that each item carries the invoice_id for the send_invoice sibling. It lacks explicit 'when not to use' or pagination/limit guidance, but the selection logic between invoice-status and job-status is clearly spelled out.

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