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

With no annotations, the description carries the full burden. It usefully discloses the authorization requirement and the six-digit code shape, and implies an outbound email side effect. It says nothing about rate limits, what happens on failed verification, or the consequences of listing, which is a real gap for a tool with email side effects.

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?

Three short sentences, front-loaded with the capability list followed by the constraint and the mode toggle. Every sentence carries information, though the 'omit email' rule slightly overlaps the first sentence's mention of listing.

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 four-parameter tool with no annotations and no output schema, the description covers the action modes and one policy constraint but omits return values, the meaning of address_id/read_token, and error/failure behavior. Adequate but incomplete.

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% across four parameters. The description compensates for two of them: email's omission toggles list mode, and code is specified as six digits (reinforcing the schema pattern). address_id and read_token remain entirely undocumented in both schema and description.

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 names three concrete operations (list contacts, request a verification email, verify a six-digit code) tied to a single resource, and the 'omit email to list contacts' clause disambiguates the modes. It is clearly distinguishable from siblings like send_email and poll_events. It loses a point only because the three-in-one framing leaves the primary purpose slightly diffuse.

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 selection rule for one mode ('Omit email to list contacts') and a policy constraint for the request mode ('only for a recipient authorized by the user'). It does not explicitly say when to supply code versus email, though that is inferable. No alternative tool is named.

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