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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=true. The description adds genuinely useful behavioral context beyond that: newest-first ordering, the exact fields returned, the explicit 'Nothing is changed or sent to a client' safety statement, and the Cotlet API key auth requirement.

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 size is reasonable and it is front-loaded, but the first two sentences are redundant: 'Invoices with client, total, amount paid and due date' is immediately repeated as 'with client, total, amount paid and due date.' That duplication wastes space without adding information.

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 full annotation coverage, complete schema descriptions, and no output schema, the description is nearly sufficient: it covers scope, ordering, safety, and auth. A little more on pagination/return shape would make it fully complete, but nothing critical is missing.

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 the schema already documents limit, cursor, and unpaid_only, including the '1 to 100. Default: 50' constraint and cursor semantics. The description's restatement of unpaid_only adds no meaning beyond the schema, so the baseline 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?

The description gives a specific verb+resource ('Lists invoices from Studio Manager') and even names the returned fields and ordering (newest first). It is clear enough that an agent knows what it does, though it does not explicitly differentiate itself from Pixieset siblings beyond the fact that the resource (invoices) is distinct.

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?

'Set unpaid_only to keep invoices that are not fully paid' gives filter-level usage guidance, and the auth prerequisite ('Needs the user's Cotlet API key with access to this app') is stated. However, there is no explicit when-to-use vs when-not guidance or reference to an alternative tool, so usage remains implied.

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