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

Annotations already declare destructive=true, idempotent=true, openWorld=true and non-read-only, so the safety profile is covered. The description adds genuinely new behavioral context beyond that: the 'Pro plan' entitlement requirement and the fact that an empty value clears forwarding. It stops short of stating reversibility or what the previous state was.

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 front-loaded sentences with no filler; the primary behavior leads and the plan note is terse at the end. The 'Pro plan.' fragment is efficient rather than wasteful.

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 non-read-only mutation tool with annotations covering the safety profile and no output schema, the description is serviceable but incomplete. It never explains what identity_id represents (the 'verified number') and gives no indication of which identity is being changed, which matters for a destructive operation.

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?

Coverage is 50%: forward_to is documented in both the schema and the description (business number on this seat, empty to stop), which is consistent but largely duplicative. identity_id is undocumented in both the schema and the description, leaving a gap the description does not compensate for.

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: it 'points a verified number at a business number' and stops forwarding when forward_to is empty. The dual-mode behavior is clear and an agent can tell this is a write operation. It doesn't explicitly distinguish itself from siblings like get_forwarding (read side) or set_number_routing, so not 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?

The empty-forward_to semantics ('stops forwarding when forward_to is empty') implicitly tells the agent how to turn forwarding off, and 'Pro plan' signals a prerequisite. However, there is no explicit when-to-use guidance or naming of alternatives (e.g. get_forwarding to read current state), so usage remains implied rather than stated.

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