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

Annotations already indicate write and destructive behavior, but the description adds crucial context: normalization to E.164, validation as a US mobile/landline, the ring_first routing configuration, and the nuance that connecting the number alone doesn't prove reachability. This goes beyond what annotations provide.

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 about five sentences, front-loading the core purpose and setup context. It's not bloated, but could be slightly tighter by removing redundant explanation of the ring_first default. Still well-structured and readable.

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?

With an output schema present, return values are covered. The description covers purpose, normalization, validation, ring_first behavior, and setup implications. It doesn't detail failure modes or error messages, but for a write operation with these annotations, this is sufficiently complete.

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 schema already documents all three parameters well. The description adds minimal extra parameter semantics—it re-explains ring_first's behavior and normalization, which are largely in the schema. Baseline 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 ('Save') and resource ('owner's own mobile number on the business record') and clearly explains the purpose (ring first, reach a human). It distinguishes from siblings like add_team_phone and attach_number by emphasizing 'owner's own' and the ring-first path.

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 context on when this is used: as part of setup, noting that a number isn't fully set up until this is on file and forwarding is verified. It also clarifies US-only numbers and the ring_first default behavior. It does not explicitly name alternatives or when-not-to-use, but the 'owner's own' scope and setup context make the use case clear.

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