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

The annotations only set readOnlyHint, idempotentHint, and destructiveHint to false; the description adds meaningful behavior: rate limits (one per minute, three per 30 minutes per phone) and the requirement that the booking be 'prepared'. This is exactly the kind of context annotations don't convey.

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?

Two sentences, zero filler; the action is first, followed by the rate limit and the usage condition. Every sentence carries necessary information.

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 two-parameter tool with no output schema, the description covers purpose, prerequisites ('prepared booking'), and critical rate-limit constraints. It does not describe the success/error response or provide fallback behavior on rate-limit hit, but that is a minor gap given the schema and annotations.

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 0% and the description never mentions confirmation_id or session_id, so it adds no meaning beyond the raw schema. While the parameter names are fairly self-explanatory, the description doesn't clarify which ID comes from prepare_booking or how the optional session_id should be used.

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 uses a specific verb ('Re-sends') and resource ('SMS confirmation code for a prepared booking'), clearly distinguishing it from sibling verification and booking tools. The phrase 'for a prepared booking' ties it to prepare_booking without needing to inspect schemas.

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 instruction 'Use only when the customer says the SMS did not arrive' is an explicit trigger condition for calling this tool. It gives clear context but does not name alternatives like start_phone_verification or specify when to choose them, so it falls short of full when/when-not guidance.

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