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

Since no annotations are provided, the description carries the full burden, and it exceeds expectations. It discloses that the tool mints a phone identity and an owner_password if not already set, returns a mobile_url and QR, and does NOT rotate an existing owner_password. It explains the response fields (owner_password_existing, owner_password) and instructs how to relay the password OOB. This is rich, actionable behavioral context.

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?

The description is long and dense but well-structured with bold headers for key concepts (owner_password handling, comparison to open_remote_control). Every sentence adds value, especially given the complexity of the tool and lack of annotations. A slight deduction for density; could be split into shorter paragraphs for easier scanning, but it remains effective.

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 tool's complexity, no annotations, and no output schema, the description covers all necessary aspects: purpose, usage context, behavior, parameter rationale, return values, and edge cases (existing vs. new owner_password). It even explains how to handle the password OOB and how the phone joins. This is remarkably complete for a tool of this complexity.

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% (all three required params have descriptions), giving a baseline of 3. The description adds extra meaning beyond the schema by explaining why session_token is needed ('required because the phone needs an identity_key to join under require_identity=true channels') and clarifying that channel_token proves authorization. This additional reasoning elevates the score.

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 clearly states the tool's function: 'Retrofit a phone-control link onto an EXISTING channel.' The verb 'retrofit' is specific and distinct from simply creating a new link. It explicitly contrasts with the sibling tool open_remote_control, listing what this tool does NOT do (mint a new channel, mint an agent identity, change trust_mode/require_identity/session_ttl), which makes the purpose unambiguous.

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 gives explicit when-to-use guidance: 'Use when agents are already in a channel and the human shows up later wanting to drive from a phone — instead of creating a new channel and migrating everyone.' It also provides an explicit comparison with open_remote_control, detailing differences in behavior. This is a textbook example of usage differentiation.

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