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 usefully adds the metric granularity (total and unique opens per country) and the underlying REST path, but says nothing about rate limits, pagination, or granularity limitations on the country breakdown.

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 compact sentences, with the substantive metric description front-loaded ahead of the API path. Nothing is padded, though the raw endpoint string adds little for an agent that only needs selection and invocation.

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 single-parameter read tool with readOnlyHint and no output schema, the description covers what is returned and how to obtain the ID. It is essentially complete, with only minor gaps around response shape and any scope limits.

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 one parameter with 100% schema description coverage, and the schema already explains campaign_id is a GUID sourced from moosend_list_campaigns. The description adds nothing beyond that, which is the expected baseline when the schema fully documents the parameter.

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 states a specific verb+resource: retrieving a campaign's opens broken down by country code, including both total and unique opens. This is clearly more specific than the sibling moosend_get_campaign_activity, though it never names that sibling to sharpen the distinction.

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?

There is no when-to-use guidance, no prerequisites, and no mention of alternatives such as moosend_get_campaign_activity or moosend_get_campaign_summary. The agent must infer from the resource name alone that this is the country-level breakdown variant.

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