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

readOnlyHint=true already covers the safety profile, and the description goes beyond it by disclosing what each mode returns: ids and key settings for the list, and full call/SMS settings plus greeting-capable voices for the detail read. That return-shape context is valuable given there is no output schema, though it doesn't address pagination or rate limits.

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 list behavior is front-loaded and the conditional detail-read mode follows. No filler, redundancy, or buried information.

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 listing/detail tool with annotations covering safety and no output schema, the description is nearly complete, explaining both the default and id-driven modes and their return contents. Only minor gaps remain (result format for the list, how large the list can get).

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 both parameters and the baseline is 3. The description reinforces the effect of passing number_id/number_pool_id and adds return-scope detail, but introduces no new syntax or constraints 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 states a specific verb (List) and explicit resources (phone numbers, number pools, caller IDs) plus the detail-read mode. It is clearly distinguishable from mutation siblings like manage_number and delete_number_item. It stops short of naming a sibling directly, so it lands just under a 5.

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 clear context for the two modes (no args to list, pass number_id or number_pool_id to drill in), which is genuine when-to-use guidance. However, it never names an alternative (e.g. manage_number for editing) or any when-not-to-use condition, so alternatives must be inferred from the sibling list.

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