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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so safety is covered. The description adds value beyond that by disclosing the return shape ('three numbers for the whole campaign') and a relative cost signal ('cheapest'), which helps an agent decide when to reach for it. Minor gap: no note on how quickly counts refresh relative to recent sends.

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 core purpose and scope front-loaded before the sibling routing. Every clause 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?

No output schema exists, and the description compensates by naming the three metrics returned (pending, completed, failed) and their granularity (whole campaign). Combined with annotations covering safety and a single fully documented parameter, nothing essential for correct invocation is 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?

The single campaignId parameter has 100% schema description coverage, including where to obtain it (campaign_list or campaign_create), so the schema does the work. The description adds nothing about the parameter, which is acceptable at this coverage level but not additive.

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 ('aggregate counts') and resource ('pending, completed and failed actions across the campaign'), and explicitly contrasts its scope with per-step and per-lead siblings. An agent can distinguish it from sequence_step_stats and sequence_leads_at_step without opening any 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?

Gives an explicit selection rule: this is the cheapest 'is it working' check for the whole campaign, while sequence_step_stats covers the same split per step and sequence_leads_at_step covers leads behind one step. Both alternatives and the condition that selects them are named.

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