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

The readOnlyHint annotation already establishes this is a safe read. The description adds the upstream endpoint (GET /accounts/{accountId}/invoices), which is mildly useful context but says nothing about pagination limits, voided-invoice handling, or the response shape. With annotations carrying the safety profile, this is an adequate-but-thin contribution.

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 sentences with zero filler; the filter scope is front-loaded and the endpoint reference is a compact trailing clause. Every part earns its place.

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 an 11-parameter read-only list tool with full schema coverage and a readOnlyHint, the description covers the what and the filter surface well. The minor gap is that with no output schema, nothing is said about returned fields or paging behavior, though the top/skip schema descriptions partly compensate.

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 all 11 parameters are already documented in the schema, including the created-date semantics of start_date/end_date and the paid/unpaid toggles. The description restates these filters at a high level but adds no syntax, mutual-exclusivity, or interaction details beyond the schema, so baseline 3 applies.

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 (List) and resource (invoices) and enumerates the available scoping filters — contact, event, event registration, paid/unpaid, created-date range. This cleanly separates it from the sibling list tools (list_payments, list_donations, list_event_registrations), so an agent can pick it without opening any schema.

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?

The phrase "optionally for one contact, event or event registration, paid/unpaid only, or within a created-date range" tells the agent when each filter applies and that all are optional. It does not, however, name an alternative or state exclusions (e.g. when to prefer list_payments), so it falls short of a 5.

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