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

With no annotations provided, the description carries the full burden and does so thoroughly: it discloses the first-wins cancellation behavior, single-billing at the winning channel's completion, the response structure (group_id, channels array with deep_link/sms_message, qr_text semantics), and the polling requirement. No behavioral trait is left ambiguous.

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 well-structured and front-loaded with the core semantics, then a clearly labeled 'Agent usage' block. Every sentence earns its place, though it is somewhat dense. It avoids fluff and redundancy, making it easy to parse.

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 no output schema, the description compensates fully: it explains the response format (group_id, channels array with deep_link/sms_message, qr_text), how to present links, and how to poll for completion. It also covers access requirements. Nothing an agent needs to call and handle this tool correctly is missing.

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%, so the schema already documents all six parameters. The description adds no additional meaning to the parameters themselves; the 'first to complete wins' behavior for the channels array is already in the schema description. 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 opens with a specific verb and resource ('Create a multi-channel phone verification') and immediately distinguishes its semantics (OR/first-wins) from any single-channel alternative. It clearly differentiates from sibling tools like create_verification by the parallel-channels behavior and the explicit mention of group_id and cancellation of losing siblings.

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?

Provides an explicit 'Agent usage' section that tells the agent exactly how to handle the response (pass deep_link to render_auth_link, print qr_text verbatim or omit, poll with get_multi_channel_verification_status). It also warns that start_login does NOT open this tool and requires a Proof account, giving clear when-to/not-to guidance.

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