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

readOnlyHint=true already tells the agent this is a safe read. The description adds that results are 'Paged' and gives the GET /bills endpoint, which is useful context beyond the annotation, but it says nothing about ordering guarantees, result-set size behavior, or how to continue past the first page (that detail lives only in the schema).

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 dense sentences: resource plus return shape first, then filters and paging, then the endpoint. Nothing is wasted and the most decision-relevant information is front-loaded.

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, listing the returned fields is a meaningful addition, and the filter/paging summary covers the 13-parameter surface. The remaining gap is that pagination continuation and default sort are left entirely to the schema, but for a read-only list tool this is close to complete.

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 13 parameters are already fully documented including enums and date formats. The description only restates the filter dimensions at a higher level (state, supplier, dates, paid status) without adding syntax or format meaning, so the schema does the heavy lifting.

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 and resource ('List bills') and immediately disambiguates the resource from the sibling invoice tools with '(purchase invoices from suppliers)'. It also enumerates the returned fields (supplier, dates, state, amount, balance, isPaid, invoice number), so an agent knows exactly what a bill is and what comes back.

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?

'Filter by state, supplier, dates or paid status. Paged.' describes capability rather than when to choose this tool over billy_get_bill or billy_list_invoices. No when-not or alternative is named; an agent must infer that this is the bulk/query path and get_bill is the single-record path.

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