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

Annotations already cover readOnlyHint, idempotentHint, destructiveHint and openWorldHint, so the safety profile is settled. The description adds genuinely new behavior: a section that fails to load returns an error without failing the rest, which tells the agent partial results are possible. It does not describe pagination or response structure, but there is no pagination here.

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?

Three sentences, front-loaded with what the tool returns, then the alternative, then the failure mode. Every sentence carries distinct information and none restates the name or annotations.

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 the burden of describing return values, and it does so concretely (counts plus four percentage rates). Combined with the disclosed partial-failure behavior and a fully documented single parameter, an agent has everything needed to call it correctly.

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?

Only one parameter and schema description coverage is 100% – the schema already states 'Numeric campaign ID (from directiq_list_campaigns)'. The description adds no meaning beyond that, so the baseline 3 applies rather than a higher score.

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 ('Summarize how a campaign performed') and enumerates exactly what comes back: recipient, open, click, bounce, unsubscribe and complaint counts plus derived rates. It also explicitly names the sibling it is not (directiq_campaign_report), so an agent can distinguish it from directiq_get_campaign 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?

The description gives an explicit routing rule: use this tool for aggregate performance, use directiq_campaign_report to see which contacts did what. That is a clear when-to-use/when-to-use-the-alternative statement. It stops short of addressing directiq_get_campaign, the other campaign sibling, leaving some ambiguity about metadata vs. stats.

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