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

With no annotations provided, the description fully carries the behavioral burden. It discloses the side effect of sending a code, the response format including the `codes-paused` failure case, the rate limit (3 calls per agent per hour), and the fact that it succeeds regardless of hub knowledge about the number. This is remarkably transparent.

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 longer than average but every sentence contributes value: purpose, flow, scope, error case, and rate limit. It is front-loaded with the core action and then explains consequences. Some structure (e.g., separate lines) could improve readability, but there is 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?

Given the simple single-parameter schema and no output schema, the description thoroughly covers necessary context: side effects, integration with confirm_booking and confirm_phone, the /me listing behavior, error handling, and rate limits. An agent has all information needed to call this tool correctly and interpret its results.

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?

Although the schema documents the phone parameter with format and length, the description adds crucial semantics: it must be the person's own number, never anyone else's, and it explains why (a code with the agent's name arrives on that phone). This goes beyond the schema's structural definition and is essential for correct invocation.

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 clearly states the action ('Tie this agent to the phone number of the person it books for') and explains the flow with a verification code and confirm_phone. It distinguishes itself from siblings by describing the linking mechanism and subsequent booking behavior, making it unambiguous which tool to use.

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 description provides clear guidance on the intended use ('Ask the person for their own number and never anybody else's') and explains the consequence of using it (bookings appear on the person's /me list). It does not explicitly mention when not to use it or contrast with alternatives like unlink_phone, but the context is strong enough to infer appropriate usage.

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