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

Annotations already cover idempotency, mutation, and open-world hints, and the description adds substantial context beyond them: the exact already_member and forwarding_loop error outcomes, the admin-secretary routing difference, and the refusal of the business's own forwarded line. This materially enriches what an agent knows 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?

Six sentences, each carrying distinct information (purpose, idempotency, role behavior, loop refusal, prerequisite, API mirror), with the purpose front-loaded. Slightly redundant with the schema's role description, and the API mirror sentence is marginal, but nothing is filler.

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 4-parameter mutation tool with full schema coverage, a rich annotations block, and an output schema, the description covers purpose, edge-case error conditions, prerequisites, and role semantics. Return-value explanation is unnecessary given the output schema exists, and no gap an agent needs to invoke correctly is missing.

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 baseline is 3; the schema already documents the role enum semantics and phone format. The description adds one genuinely parameter-level fact — that the business's forwarded office line is refused for phone_number — but otherwise mostly restates role behavior already present in 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 first sentence states a specific verb ('Add'), a specific resource ('the phone system's team ring group'), and the operational goal (rings before Kai answers). It clearly differentiates from siblings like attach_number and set_owner_phone by scoping this tool to the ring-group membership action.

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 provides explicit context: it covers both teammates and owners/admins, notes idempotency behavior, and names the prerequisite set_up_phone_system. It stops short of explicitly contrasting with siblings (e.g., when to use set_owner_phone instead), so it lacks an exclusion-based routing statement.

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