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

Annotations already provide readOnlyHint, idempotentHint, and destructiveHint=false, and the description confirms 'Side effects: none (read-only).' It adds useful behavioral context about the fax pipeline and that the agent should not prompt the user, exceeding what the structured fields convey.

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?

Three short sections: purpose, workflow instruction, and side-effect note. It is front-loaded and every sentence adds either semantics or safety/usage guidance.

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?

Given the simple list operation, zero required parameters, full schema coverage, and presence of an output schema, the description plus annotations cover what an agent needs to invoke it correctly, including its role in the fax flow.

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 schema already documents user_id default and pipeline_id provenance/passing. The description adds only a light contextual mention that pipeline_id is optional and tied to pipeline_start, not enough to move beyond the baseline.

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 opens with 'List your purchased or assigned phone numbers,' a specific verb, resource, and scope. It clearly distinguishes from sibling tools like get-number (single number) and update-number (mutation).

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?

It gives explicit workflow guidance: call after pipeline_start and before request-file-from-user when sending a fax, and instructs the agent not to ask the user to pick a number. This is direct when-to-use and when-not-to-behave instruction.

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