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

Annotations only declare readOnlyHint=true, so the description earns credit for disclosing the hard rate limit of 2 calls per 60 seconds per API key and the paging bounds (default 50, max 1000). That is genuine behavioral context an agent needs to plan calls. It stops short of describing the response shape or ordering of results.

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-loaded with the core purpose, then types, paging/date behavior, and the rate limit in a compact NOTE. The REST path reference is arguably redundant given the tool already calls it, but it is short and does no harm.

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 more burden than it does here: it never characterizes the return payload (fields per recipient, ordering, empty-result behavior). Rate-limit, paging, and type coverage are solid, so it is adequate but has a clear gap on the output side.

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 coverage is 100%, so baseline is 3, but the description adds two facts not fully in the schema: the page_size default of 50 and the 'Activity (all)' semantics of the type enum, plus the date-filtering behavior. This meaningfully reinforces the parameter contract rather than just restating it.

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+resource ('per-recipient activity for a campaign') and enumerates the exact activity types, so the scope is unambiguous. It does not, however, explicitly distinguish itself from close siblings like moosend_get_campaign_link_activity or moosend_get_campaign_summary, leaving the agent to infer the boundary.

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 gives operational context (paging defaults, date filtering, rate limit) but offers no explicit when-to-use guidance or alternatives relative to the sibling activity/summary tools. Usage is implied by the 'per-recipient' framing rather than stated.

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