attachPhoneNumber

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

Annotations already indicate readOnlyHint=false and destructiveHint=false. The description adds useful context about 'account-owned' phone numbers and 'existing agent,' but omits side effects, failure modes, or multi-attachment behavior. Adequate but not thorough.

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 main sentence is concise and front-loaded, but the trailing '(Tags: Phone numbers)' is extraneous and does not earn its place. Otherwise, the structure is efficient.

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?

The operation is simple: one nested object with two well-documented parameters, no output schema. The description provides the key constraints (account-owned, existing agent). Could mention whether the number must be unattached, but is otherwise complete for this scope.

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 description coverage is 100% for both parameters (agent_id, phone_number_id), so the schema fully documents them. The description adds no additional parameter-level detail, justifying the baseline score of 3.

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 specific action: 'Attach an account-owned phone number to an existing agent.' This distinguishes it from the sibling tool 'detachPhoneNumber' and accurately conveys the resource being modified.

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?

Usage is implied by the action, but the description does not explicitly state when to use this tool versus alternatives like 'detachPhoneNumber' or any prerequisites/exclusions. No when/when-not guidance is provided.

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