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

Annotations already declare this is a non-read-only, idempotent, non-destructive operation, so the description only needs to add context. It usefully discloses the side effect that list_name can create a new list and that alert-enabled lists email the user on role posts or funding rounds, but says nothing about auth needs or duplicate-add behavior.

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, front-loaded with the action, then the parameter guidance, then the side-effect note. No filler; the final sentence about alerts is slightly tangential but still earns its place as behavioral context.

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-parameter mutation tool with no output schema and no annotations covering side effects, the description covers the essential targeting logic and the notable list-creation/alert behavior. Remaining gaps (duplicate handling, permission requirements, error responses) are minor.

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 coverage is only 33% (list_id and list_name have no schema descriptions), so the description must compensate, and it does: it defines the list_id/list_name alternatives and clarifies that list_name doubles as a list-creation mechanism. It does not disambiguate precedence if both are passed, which keeps it short of a 5.

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 ("Add a startup to one of the user's lists") that is immediately distinguishable from the sibling remove_from_list and from list_lists. An agent knows exactly what operation this performs 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?

Explains the two mutually exclusive ways to target a list (list_id or list_name) and that list_name may name either an existing list or a new one to create. It gives clear usage context but never states when not to use it, e.g. what happens if both are supplied or if the company is already tracked.

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