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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds real value beyond that: the monthly granularity, the warning that an unfinished month is incomplete, and the authentication requirement ('Cotlet API key with access to this app').

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 first two sentences overlap heavily: the field list ('VAT, fees, taxes, products sold and affiliate payouts') is then restated as the seven items in full detail. This redundancy wastes space, though the auth and incompleteness caveats are well placed at the end.

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, single-parameter tool with no output schema, the description supplies the field breakdown, the monthly limitation, and the credential requirement, which is close to what an agent needs to call it correctly. Only the relation to the sibling sales-stats tool 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?

There is a single required parameter with 100% schema coverage, so the schema already documents the YYYY-MM format. The description adds only the implied monthly framing, not format or edge-case syntax beyond what the schema states. 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?

The description names a specific verb+resource (get the monthly sales report) and enumerates the exact fields returned, so an agent knows precisely what it produces. It does not explicitly differentiate from the sibling payhip_get_sales_stats, leaving some ambiguity about which report tool to pick.

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?

Usage is implied by 'monthly report' and the caveat that an unfinished month is incomplete, which hints at when it is appropriate. However, it never names an alternative or states an explicit when-to-use/when-not condition, and the nearby payhip_get_sales_stats sibling is ignored.

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