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

Annotations already state readOnly=false, destructive=false, idempotent=true, but the description adds value beyond them: in-flight messages handed to the carrier cannot be recalled, the held allowance stays held, the Send Message module prerequisite, and an explicit 403 'module not enabled' do-not-retry directive. That is exactly the behavioral context an agent needs before calling.

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?

Front-loaded with the core action and its immediate limitation, then layers alternatives and error handling in a logical order. Sentences are dense and each carries distinct information, though the error-handling tail is long enough that a reader must work through it.

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 state-mutating tool with no output schema, the description covers the mutation semantics, reversibility, allowance behavior, prerequisite, error path, and sibling routing. An agent has everything needed to invoke it correctly and handle failure.

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 with 100% schema description coverage, so the schema already carries the UUID v4 format and the 'queued or sending' status constraint. The description reinforces the status eligibility but adds no syntax or format detail beyond the schema, matching the baseline-3 case for high coverage.

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 precise verb and resource ('Stop a campaign') and immediately scopes it to the 'queued or sending' states. It is clearly distinguished from resume_campaign and cancel_campaign by naming both siblings and their distinct effects.

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?

Explicit when-to-use and when-not: use resume_campaign to continue, cancel_campaign to release the allowance and end it permanently. It also routes the agent to fetch_messaging_usage for refused sends, with the exact reasoning ('it is what distinguishes module access, plan channels...'). Nothing is left to inference.

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