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

The description discloses the key behavioral trait beyond annotations: each contact belongs to exactly one list, so the call REASSIGNS list_id and is a move, not a copy. It also states what the call returns, which is valuable because there is no output 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?

Three sentences with no filler: the core operation is front-loaded, followed by the crucial caveat, a practical use case, and the return behavior. Every sentence earns its place.

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 fully documented schema and no output schema, the description covers how to obtain list_id, the reassignment semantics, when to use it, and what it returns. Nothing essential is 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 input schema already describes both parameters with 100% coverage, so the baseline applies. The description adds the source of list_id (list_lead_lists) and clarifies contacts must already exist, but these are supplemental rather than necessary.

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 verb and resource ('Move existing contacts into an existing lead list') and adds the critical distinction that this is a reassignment, not a copy. This clearly separates it from the similarly named add_contacts_to_campaign sibling.

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 a concrete use case (moving leads out of 'CRM Imports' into a named list) and explicitly places the call before add_contacts_to_campaign. It does not explicitly list when not to use it, but the intended context is clear.

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