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

readOnlyHint=true already declares the safe-read profile, so the bar is lower. The description adds the REST mapping (GET /payment/invoices), confirming a non-mutating read, but says nothing about pagination semantics, auth requirements, or result shape beyond what the schema and annotation imply.

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, purpose front-loaded, nothing wasted. The REST endpoint line is arguably marginal but costs almost nothing and is not distracting.

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, fully-documented, zero-required-param read tool with an annotation covering safety and no output schema to explain, the description is sufficient. Only minor gaps (pagination behavior, result format) remain.

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%, with limit, invoice_type, and starting_after all documented inline, including the pagination cursor. The description adds no parameter detail, so the baseline 3 is correct — the schema carries the full load.

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+resource+scope: 'List billing invoices for the account', which is unambiguous and maps to a resource none of the siblings cover. It stops short of explicitly differentiating from billing-adjacent siblings like get_usage or get_usage_rent, so it lands at a clean 4 rather than 5.

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 implied by the listing verb and account scope, but there is no explicit when-to-use guidance, no exclusions, and no routing against the several other billing-shaped siblings (get_usage, get_usage_rent, get_rate_limit). Minimum-viable, with the agent left to infer the choice.

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