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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description adds genuinely new context: the returned fields, the semantics of the sent/viewed flags mapped to the blue letter and purple eye icons, and an authentication requirement ('Needs the user's Cotlet API key with access to this app'). It omits pagination behavior for a list endpoint, 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?

Front-loads the core purpose and result fields, with each sentence adding something (fields, scope, flag interpretation, auth). The UI-icon sentence is slightly redundant with the flags sentence but still earns its place as an interpretation aid.

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 description carries the return-value burden and does so reasonably by enumerating the invoice fields and flag semantics. Parameter coverage is fully handled by the schema, and annotations cover safety; only pagination/total-count behavior is left unstated.

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 both the tab enum and page number are already documented with defaults in the schema. The description restates the unpaid/paid tab concept but adds no syntax or format detail beyond it, matching the baseline 3 when 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 (lists invoices) and names the returned fields (customer, total, balance, sent/viewed flags). It scopes the result set to the Invoices page tabs, which makes the intent clear, though it does not explicitly distinguish itself from sibling kickserv tools like generate_invoice or send_invoice.

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?

The description implies usage through the tab mechanics (unpaid vs paid tab), so an agent can infer this lists existing invoices. However, it names no alternatives and gives no explicit when-to-use or when-not-to-use guidance.

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