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

readOnlyHint=true already declares the safety profile, so the description need not restate that it is a safe read. It adds genuine value by enumerating the returned field set (id, number, client_id, status, currency, date, due_date, subtotal, total), which compensates for the absent output schema; truncation behavior is left to the schema rather than the description.

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 compact segments with zero waste: the purpose and return fields come first, followed by the Paymo endpoint. Nothing is padded or redundant.

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 inline field enumeration usefully conveys the return shape, and the schema fully covers inputs. The only shortfall is the absence of usage/routing guidance, which is minor for a straightforward read-only list tool.

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 four parameters (limit, where, status, client_id) are already fully documented in the schema. The description adds no parameter syntax or semantics beyond what structured data provides, so the 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 clear verb+resource ("List invoices") and enumerates the returned fields, so the agent knows it is a collection read against the Paymo invoices endpoint. It does not, however, distinguish this from the sibling paymo_get_invoice tool or clarify the list-vs-single relationship.

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?

No when-to-use, when-not, or alternative guidance is given. The agent is not told to prefer this over paymo_get_invoice for a single record, nor that the typed filters (status, client_id) exist as the intended narrowing mechanism.

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