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

Annotations already declare this is a non-read-only, non-destructive, idempotent, closed-world write. The description adds genuinely non-structured facts: the operation is free, locked people are silently skipped, and personalised lines are carried along with the saved leads. It does not explain what happens on a name collision with an existing list.

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 tight sentences with the action and both targeting options front-loaded. 'Their personalised lines go with them' is slightly conversational but conveys a real side effect, so little is wasted.

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 3-param write tool with no output schema and 0% schema coverage, the description covers the core behaviors an agent needs (unlocked-only, free, carries personalised lines, two list-targeting modes). Missing only edge-case behavior such as duplicate/idempotent handling and name-conflict resolution.

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%, so the description carries the burden and does explain the two list parameters (list_id = existing list, list_name = new list). lead_ids is left to the schema, and required/optional status is not stated, but the meaning of the ambiguous params is supplied.

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?

Specific verb+resource: saves unlocked Intent people to a prospect list, with the two targeting modes (existing list_id vs new list_name) named inline. It is distinguishable from write-adjacent siblings like unlock_intent_leads or list_intent_leads, though it never names an alternative tool directly.

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 a clear precondition (only unlocked people are saved; locked ones are skipped) and implicitly routes the caller between supplying list_id for an existing list or list_name for a new one. No explicit when-not-to-use or named alternative is offered, which keeps it short of a 5.

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