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

Annotations already declare readOnlyHint=true, idempotentHint=true, openWorldHint=true, destructiveHint=false, so the safety profile is fully covered. The description adds the pagination ceiling and the optional date window, but says nothing about ordering, default sort, or empty-result behavior. With annotations carrying the behavioral load, a 3 is right.

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 clauses with zero filler; the core purpose and returned fields come first, with the pagination/date constraints trailing in a compact fragment. Every element earns its place.

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, paged listing tool with full schema coverage and no output schema, naming the returned fields (email, name, lists, time) is the key missing piece and it is supplied. Minor gaps are sort order and whether contacts with multiple clicks are deduplicated.

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 including campaign_id and the date format is already documented in the schema. The description only restates limit and date_from/date_to, adding no semantics beyond the structured fields. Baseline 3 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?

States a specific verb and resource ('List the contacts who clicked a link in a campaign') and enumerates the returned fields, which cleanly separates it from get_campaign_opens and get_campaign_unsubscribes. An agent can pick this over its siblings without opening a 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?

Usage is only implied by the pagination and date-filter hints ('Paged (limit 1-100); optional date_from/date_to'). There is no explicit when-to-use, when-not-to-use, or pointer to a sibling such as get_campaign_opens for open data.

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