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

With no annotations, the description carries the full burden of behavioral disclosure. It states the action and access needs but does not mention side effects (e.g., what happens to the previous primary phone), prerequisites (phone must exist), or reversibility. This is a significant gap for a mutation tool.

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 short and front-loads the purpose in the first sentence. The access note is useful but slightly verbose (mentions Claude Code path); overall it is concise and well-structured.

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 single-parameter tool with no output schema or annotations, the description is acceptable but not complete. It covers purpose and access, but omits behavioral details like whether the phone must already exist or what happens to the prior primary. An agent could call it correctly with schema help, but the description could do more.

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%, so the parameter 'id' is already documented as 'Phone record ID to set as primary'. The description adds nothing beyond the schema, so the baseline of 3 is appropriate.

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 states a specific verb and resource: 'Set a phone number as the primary phone for the account.' This clearly distinguishes it from siblings like set_primary_email and set_primary_profile by naming the target resource (phone number) and the intent (primary for account).

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 access prerequisites (needs a Proof account, authentication options) but does not explicitly explain when to use this tool versus alternatives. It implies usage from the purpose but lacks explicit routing or exclusions, so it is minimally adequate.

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