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

Annotations already cover the safety profile (readOnlyHint=true, destructiveHint=false), so the description's job is to add context — and it does by disclosing the return shape ('counts and first/last event time'), which matters because there is no output schema. It stops short of mentioning pagination behavior or result size limits.

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 sentences, zero waste, with the scope/what-is-returned information front-loaded and the 'exactly one event' constraint immediately after. Nothing redundant beyond the necessary endpoint reference.

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 listing tool with no output schema, the description covers the return fields and the single-event selection rule, so an agent has enough to call it correctly. Minor omission: no mention of pagination or expected result volume, though the schema's offset hint partially compensates.

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 every parameter is already documented and the baseline is 3. The description's prose enumeration of event values restates the enum rather than adding new syntax or format detail, so it does not lift the score above baseline.

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 ('Per-contact engagement for a sent campaign') and enumerates the exact engagement slices returned, which implicitly separates it from aggregate siblings like get_campaign_counts and get_campaign_links. An agent can tell what it returns without opening the schema.

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?

It gives one hard usage constraint ('Pick exactly one event') and the backing endpoint, but says nothing about when to prefer this over get_campaign_counts/get_campaign_links or what prerequisites (e.g., campaign must be sent) apply. Usage is implied rather than guided.

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