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

Annotations provide readOnlyHint=false, destructiveHint=false, but description adds critical behavior: initiates external SMS challenge, is intentional for harnesses, and gives security warnings (do not log code, do not paste OTP). This is essential context beyond annotations.

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?

Concise, front-loaded with action and scope, then error conditions, then next steps, then warnings. Every sentence adds value; zero fluff.

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?

Despite no output schema, description fully covers error conditions, next step, alternatives, and sensitive data handling. An agent can successfully invoke and follow up.

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 has 100% coverage with both parameters described (phone, tenant_code as part of request body). Description does not re-explain them, but adds the 'scoped by tenant_code' meaning, which is slightly beyond 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?

Clear verb 'start' with resource 'Twilio Verify SMS login challenge' to 'phone', scoped by tenant_code. Distinguishes from siblings like requestOtp and login.

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?

Explicit next step (call login with provider phone_otp), error conditions (400 if not configured/rate-limited), and mentions SIWE as preferred alternative. Perfect when-to-use guidance.

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