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

With no annotations, the description carries the full behavioral burden and does so: it discloses the only side effect (sends an email), that nothing is created, the code lifetime (10 minutes), the attempt limit (5 tries), the resulting 60-minute reusable session token, and the privacy property that a code is sent regardless of whether the address has watches. This is exactly the behavior an agent cannot infer from a one-parameter schema.

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?

Four sentences, front-loaded with purpose before prerequisites, then expiry/attempt limits, then the privacy rationale. Every sentence conveys a fact an agent needs; there is no filler or restatement of the name.

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?

No output schema exists, so the description must explain outcomes, and it does: the downstream 60-minute session token and the deliberate non-disclosure of watch existence. For a one-parameter, annotation-free tool this leaves nothing an agent needs missing.

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 single parameter has 100% schema description coverage ('Email address to send the code to'), so the schema already handles the basics and the baseline applies. The description adds only marginal parameter meaning, notably that an email with no watches still receives a code, which is behavioral context rather than syntax.

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?

States a specific verb and resource ('Send a 6-digit verification code to an email address') plus the scope ('for watch access'), which immediately separates it from the sibling watch tools and from domain/mark screening tools. An agent knows exactly what this does without opening the schema.

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?

Gives explicit ordering ('Call it BEFORE list_watches, unwatch_mark, or attaching an email to a watch with watch_mark') and names the exact siblings it precedes. This is a clear when-to-use rule with the alternatives identified, not implied usage.

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