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

readOnlyHint=true already tells the agent this is a safe read, so the description is not carrying the safety burden. It adds the underlying endpoint (GET /invoices), but says nothing about pagination behavior or result ordering, which would be genuinely useful for a 7-param list tool.

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, front-loaded with the action and filters, with the API endpoint appended as useful routing context. No filler, though the endpoint clause is the only marginally optional element.

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 read-only list tool with full schema coverage and an annotation covering safety, no output schema is strictly needed and nothing essential is missing. A note on pagination or default page size would round it out.

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 each of the 7 parameters documented (status enums, date formats, external_customer_id). The description merely echoes those filter categories, adding no syntax or format detail 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+resource ('List invoices') with the filterable dimensions called out, so an agent knows exactly what it retrieves. It does not explicitly distinguish itself from the sibling lago_get_invoice (singular), but the list-vs-get distinction is unambiguous.

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 filtered by...' implies the retrieval context and enumerates usable filters, giving implied guidance on when this tool applies. However, there is no explicit when-to-use vs when-not, and no pointer to lago_get_invoice for single-record lookups.

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