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

Annotations already signal mutation (readOnlyHint=false, destructiveHint=true), and the description adds the specific side effect: 'adds a member to the number's assigned_to list.' It does not detail edge cases such as duplicate assignment or failure behavior, but it goes beyond the annotations without contradicting them.

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 compact and front-loaded: action and side effect first, then parameter clarification, then the critical revoke-number warning. No sentence is wasted and every part contributes to correct invocation.

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 3-parameter nested payload, full schema coverage, output schema, and annotations, the description covers what remains: the exact assignment effect and the revoke alternative. An agent has enough context to call this tool correctly without additional assumptions.

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% and the schema already documents number and payload. The description adds practical context beyond the schema, such as 'user_id is the number owner/account context (usually self for the admin)' and 'payload.assigned_to is the member user ID to assign TO', which helps an agent pick the right owner versus target.

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 opens with a concrete verb and resource: 'Assign a fax number to a corporate member' and specifies the underlying effect ('adds them to assigned_to'). It also differentiates itself from revoke-number by naming the sibling and the opposite action, so an agent can distinguish it immediately.

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 direction for when to use this tool versus the alternative: use revoke-number with that member's user_id to remove, while warning not to use revoke-number with self unless removing your own assignment. It also clarifies user_id as owner/account context, aiding correct invocation.

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