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

readOnlyHint=true already declares the safe read profile, and the description is consistent with it. The description adds the useful detail that results are total AND unique opens grouped by country, but says nothing about permissions, date-range behavior, or response shape beyond the grouping dimension.

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 short, front-loaded sentences with no filler; the resource meaning comes first. The trailing 'Moosend: GET /campaigns/{CampaignID}/stats/countries.json' is slightly redundant implementation detail but cheap and harmless.

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 correctly communicates what the tool returns (opens by country code) and the tool is a single-parameter read operation, so most of what an agent needs is covered. Minor gaps around result ordering or empty-result behavior keep it from a 5.

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% and the single campaign_id parameter is fully documented in the schema as a GUID sourced from moosend_list_campaigns. The description adds no additional parameter meaning, so the baseline 3 for schema-driven params 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 names a specific resource (a campaign's total and unique opens) and a specific dimension (broken down by country code), which an agent can distinguish from sibling tools like get_campaign_activity or get_campaign_summary. However, it never explicitly contrasts itself with those siblings, so the differentiation relies on inference.

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 statement of when to use this tool versus get_campaign_activity, get_campaign_link_activity, or get_campaign_summary. The agent must infer the selection rule purely from the resource phrase, and no exclusions or prerequisites are given.

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