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

Beyond the annotations, the description reveals critical behaviors: the code is not returned to the agent, it goes to the user's own inbox/phone, it expires in 5 minutes, it covers one booking, and sending is rate-limited. This is exactly the kind of behavioral context the annotations do not provide.

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 front-loaded with the core action and uses clear sections for usage and behavioral notes. It is somewhat longer than strictly necessary, but each part serves a purpose, especially the 'YOU DO NOT RECEIVE THE CODE' warning and the anti-loop guidance.

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?

The description fully covers when to call, what happens when called, what the agent should expect (and not expect), how the code behaves, and important limits. Even without an output schema, the agent has enough context to invoke the tool correctly and interact with the user appropriately.

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?

The schema already describes all three parameters with 100% coverage, including the choice between email and phone and the phone format preference. The description adds context about contact ownership but does not materially change or deepen the per-parameter semantics beyond what the schema provides.

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: 'Send the user a 6-digit confirmation code.' It also explicitly links the tool to its sibling book-appointment by noting the code is required before booking, which distinguishes it from the other tools in the list.

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 WHEN TO USE section gives concrete preconditions: the user has chosen a venue, service, and slot, and has provided email or phone. It also specifies ordering ('Call this before book-appointment') and warns against looping, giving the agent clear action boundaries.

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