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

Annotations already mark the tool as non-read-only, non-idempotent, and non-destructive. The description adds useful behavioral context by disclosing the SMS side effect and requiring explicit user consent before calling. It does not mention rate limits or code expiration, but those are not essential for basic correct invocation.

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 compact and front-loaded with the core action, followed by clear usage conditions, next steps, and an alternative. Every sentence carries useful information with no repetition or filler.

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 simple one-parameter tool with no output schema, the description is complete: it explains the action, when to call it, what to do after the SMS is sent, and how it relates to a sibling tool. An agent has enough context to invoke it correctly.

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 the phone parameter with format hints and length constraints. The description adds no additional parameter semantics beyond what the schema provides, landing at the baseline 3.

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 action and resource: sending a verification code SMS to the user's phone as signup step 1. It also distinguishes itself from sibling tools by naming the follow-up (signup) and the alternative payment path (create_checkout).

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?

It gives an explicit trigger condition: only call when the user clearly says they want to sign up. It also provides routing guidance by noting create_checkout can be used without signup, and tells the agent to ask the user for the code and pass it to signup.

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