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

Annotations already declare read-only/idempotent/non-destructive, but the description adds substantial behavioral context beyond them: pagination defaults (25, max 100), personal-data handling instructions, explicit 403 gating semantics ('read-only and NOT gated by the Send Message module'), and a diagnostic hint if 403 still occurs. This is exactly the kind of rich disclosure the annotations don't cover.

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?

The description is front-loaded with purpose and pagination, then moves to search/status usage, privacy, and error handling. Every sentence carries information, though the final 403 sentence is dense and could be tighter. It is efficient but not maximally structured.

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, paginated list tool with no output schema, the description covers what an agent needs: purpose, pagination limits, exact-search constraint, status filter rationale, privacy handling, and 403 behavior. Nothing required to invoke it correctly appears missing.

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 all five parameters (including exact-search semantics and pagination limits) are already documented in the schema. The description restates the search-exactness and pagination defaults, adding no syntax or format detail beyond what the schema provides, so the 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?

The description opens with a specific verb and resource: 'List who a campaign went to and what happened to each message, paginated.' This clearly distinguishes it from siblings like fetch_campaign_report (aggregate metrics) and fetch_campaigns (campaign list) without needing to name them.

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 explicit operational guidance: 'search takes ONE EXACT email address or phone number, not a fragment — use the status filter to narrow, not search.' This tells the agent how to choose between search and status. However, it never names an alternative tool or states when not to use this one, so it falls short of the 5 benchmark.

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