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

Annotations already declare readOnlyHint=true, non-destructive and open-world, so the safety profile is covered. The description adds real behavioral context beyond them: private notes are withheld by default and only exposed via include_private_notes, and it discloses which fields the response carries. It omits pagination/limit behavior, which keeps it from a 5.

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?

Three dense sentences with the returned-field inventory front-loaded, followed by filterable dimensions and the private-notes caveat. The field enumeration is long but every clause maps to real behavior; no filler text.

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 15 parameters, no required params, and no output schema, the description usefully enumerates the returned fields and the default-hiding of private notes, which is what an agent most needs. It leaves pagination/limit semantics and the include_custom_fields behavior to the schema, which is acceptable given the schema coverage.

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 80%, so the schema already documents most parameters. The description's filter list (client, project, user, invoice, date range, billing status, exact expense type) loosely maps to the undocumented user_id/client_id/billing_status parameters, adding only marginal meaning beyond the schema. Baseline 3 is appropriate.

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') plus resource ('expenses') and enumerates what is returned (client, project, user, expense date, cost, sell price, quantity, type, billing status, invoice id, public description). It also names the exact filter dimensions and the underlying endpoint GET /expenses, making it clearly distinguishable from siblings like bill4time_list_invoices or bill4time_list_time_entries.

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?

Gives concrete usage context: which dimensions can be filtered and that private notes are hidden unless the flag is set. It does not, however, state when this tool should be preferred over a sibling (e.g., when to reach for invoices vs expenses) or any exclusion conditions, so it stops 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.