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

Annotations already cover readOnly, idempotent, non-destructive and closed-world, so the safety profile is established. The description adds genuine value by clarifying that no outbound messages are sent and no message content is retrievable, which is not in the annotations. It stops short of noting rate limits, latency, or aggregation behavior.

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?

A single compact sentence with the capability front-loaded and a scope caveat trailing after the semicolon. No filler and nothing redundant with the title 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 an output schema, full parameter documentation and rich annotations already present, the description only needed to establish scope and side-effect freedom, which it does. Missing only a note on how results are framed (per-day buckets, retention limits) that would make it fully self-sufficient.

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%, and each of the three parameters (days, agent_id, channel_id) is documented inline, so the baseline 3 applies. The description's 'daily' wording corroborates the granularity implied by the days parameter but adds no format or constraint 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?

States a specific verb-and-resource pair: reports daily incoming/outgoing counts. The negative clause ('no customer messages are sent or reconstructed') sharpens the scope to aggregates rather than message content. It does not, however, distinguish itself from close siblings such as line_events_read or line_health_read, leaving the agent to infer the boundary.

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 only implied: the 'no messages are reconstructed' clause implicitly excludes using this tool to inspect message content, which nudges toward line_events_read for that need. No explicit when-to-use statement, prerequisites, or named alternative appears.

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