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

Annotations already declare readOnlyHint=true and destructiveHint=false, and the description adds substantial non-obvious context: balance due is total minus recorded payments, due date is creation date plus Payment Terms, overdue mirrors the Joist badge, and each item shows email-opened and signed status. It also flags the Cotlet API key requirement, which annotations do not cover.

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?

The core purpose and view scoping are front-loaded in the first sentences, and the field-semantics follow. The field enumeration at the start is somewhat listy, but nearly every sentence carries unique information with no filler.

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 read-only list tool with complete annotations and full schema coverage, the definition is nearly complete: safety is covered by annotations, parameters by the schema, and the description explains the returned fields' semantics well. Minor gaps remain around pagination behavior and result volume, which the cursor parameter only implies.

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 coverage is 100%, so the baseline is 3, but the description elaborates the semantic meaning of the view values ('not paid in full') and explains the derived fields that the limit/cursor/search parameters operate over, adding value beyond the schema text.

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 ('Lists invoices'), names the fields returned, and scopes it to the Active or Paid view with newest-first ordering. An agent can distinguish it from the many sibling list_invoices tools via the joist_ prefix, though it doesn't explicitly contrast with joist_list_estimates or joist_get_document.

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?

Explains the two view modes clearly ('Active view (not paid in full) or the Paid view') and the default, giving the agent enough to pick a view. It stops short of explicit when-not-to-use guidance or naming an alternative sibling, so it falls just below a full 5.

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