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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds a concrete API endpoint (GET /v1/campaigns/{campaign_id}/metrics) and the notion of 'over time,' but does not disclose behavior like returned metric types, pagination, or time-range constraints beyond that.

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 tight sentences: the first states the core purpose, and the second gives the exact API route. No filler or redundant explanation, and the most important information is front-loaded.

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 metrics tool with fully documented parameters and no output schema, the description provides enough context: it identifies the metric category (delivery/engagement), the time-series nature, and the endpoint. It does not describe the return shape, but that is less critical given the otherwise strong schema and annotation coverage.

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?

Input schema coverage is 100%, so parameters like period, steps, and type are already documented. The description only restates campaign_id in the endpoint path and adds no further semantic detail beyond the schema.

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 uses a specific verb and resource: 'Get delivery/engagement metrics for a campaign over time.' This clearly distinguishes it from sibling tools like customerio_get_campaign, which would fetch campaign details rather than metrics.

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 states what the tool does but gives no guidance on when to choose it over alternatives, such as customerio_get_campaign for campaign details or customerio_list_campaigns for campaign discovery. No exclusions or alternative routes are mentioned.

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