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

Annotations only cover mutation/safety hints (readOnly=false, idempotent=false). The description adds the critical traits annotations cannot express: 5-minute code validity, 5-attempt limit, hard rate limits (1/60s, 5/day per number, 10/day per user), binding is permanent per account, and numbers bound elsewhere are refused. Exceptional behavioral disclosure.

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?

Front-loaded with the core action, then constraints and warnings in a logical sequence. Dense but every sentence earns its place given the number of behavioral caveats. Slightly long, but the density is justified for a tool with real foot-guns.

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?

No output schema exists, and the description covers the full lifecycle: what's sent, how to complete verification, error conditions (already-bound number), retry guidance (wait when limited), and identity model. An agent has everything needed to call it correctly and safely.

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 single parameter is fully described in the schema (including mainland vs. international format). The description adds context about which number to supply (caller's own, not someone else's) and international country-code requirements, but this overlaps with the schema. Baseline 3 for high coverage 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?

States a specific verb+resource (send a 6-digit SMS code to the user's own phone) and names its scope: real-name verification binding the caller's own number. The pairing with verify_phone_code is made explicit, distinguishing it from any other sibling.

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 explicit when-to-use (user has explicitly asked to verify) and when-not-to-use (never on your own initiative, don't fill in someone else's number), plus the follow-up tool. This is a textbook routing instruction.

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