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

readOnlyHint=true already establishes this is a safe read. The description adds the return field set and the REST endpoint, but omits behavioral facts like truncation/no-pagination policy (which lives only in the schema). Adequate but thin beyond annotations.

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 with the endpoint as trailing detail. No wasted words, though the parenthetical field list is somewhat dense.

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, naming the returned fields is genuinely useful for the agent. Combined with rich filter descriptions in the schema, the definition is nearly complete; only usage guidance and truncation behavior are unaddressed in prose.

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 seven filters (limit, where, date_from/to, invoiced, client_id, project_id) are already fully documented. The description adds nothing about filter semantics, so the baseline of 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 expenses') and enumerates the returned fields, plus the underlying endpoint GET /api/expenses. It is distinguishable from siblings such as paymo_list_invoices and paymo_list_clients by resource, though it never explicitly contrasts them.

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 guidance on when to use this versus alternatives, no prerequisites, no mention of auth or context. The agent must infer usage purely from the name and resource.

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