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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so safety is covered. The description adds genuinely useful behavior beyond that: the 404 when no plan exists, the shape of the returned data (installments with dates, amounts, balances, approval status), and the underlying endpoint.

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 tight sentences: payload first, then failure mode and endpoint. Nothing is redundant and the most decision-relevant information (what it returns) leads.

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 read with no output schema, the description covers resource identity, return payload, error case, and endpoint. The only gap is that return values are only summarized rather than typed, which is acceptable but keeps it out of the top band.

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% for the single invoice_id parameter, so the schema already documents it fully. The description adds no format, range, or sourcing detail beyond what the schema supplies, which is the expected baseline when the schema does the work.

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 names the specific resource (the payment plan attached to an invoice) and enumerates its payload, which implicitly separates it from the sibling invoiced_get_plan (a plan catalogue) and invoiced_get_invoice. It stops short of naming those siblings outright, so differentiation is inferable rather than explicit.

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?

Usage is only implied: the agent can infer this is the tool for fetching one invoice's installment schedule, but there is no statement of when to prefer it over invoiced_get_invoice or invoiced_get_plan, and no prerequisites. The 404 note is a failure condition, not routing guidance.

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