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

Annotations already declare readOnly, idempotent, non-destructive, and openWorld, so the safety profile is covered. The description adds real behavioral context beyond them: the default 30-day window when no dates are supplied, and the caveat that calls/leads are only present 'where tracked', which tells the agent to expect missing metrics.

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 compact sentences with the resource and metrics front-loaded and the date default last. No redundant restatement of the title and no filler.

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 explaining return values, and it does so by enumerating spend, impressions, clicks, and calls/leads. It is slightly thin on return shape (per-channel grouping structure, whether zero-value channels appear), but an agent can 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?

Schema coverage is 100%, so the baseline is 3. The description earns an extra point by documenting the default date window, which the schema does not state for from/to, and by indicating that results are grouped per channel rather than returned flat.

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 resource (results for one campaign) and its granularity (by channel), plus the exact metrics returned. An agent can distinguish this from my_campaigns, which lists campaigns rather than reporting on one. It stops short of naming a sibling explicitly, so it is clear but not fully differentiated.

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 implied: you fetch results for a single campaign identified by order_id, and the 30-day default gives a sensible no-argument call. There is no explicit when-to-use or when-not-to-use guidance, and no pointer to my_campaigns as the source of order_id in the description (only in the schema).

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