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

Adds substantial context beyond the annotations: the change is non-destructive in scope (existing channels keep their captured values), it requires marketing-automation write access, and it can return PERMISSION_DENIED or DISCONNECTED. The annotations only declare readOnly/destructive/openWorld flags; the description tells the agent what the mutation actually touches and what conditions can cause failure.

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 short sentences with no filler. The core write action and its parameter source come first, followed by the effect scope, failure modes, and permission requirement in a logical order.

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, but the description covers the return shape (updated setting or PERMISSION_DENIED/DISCONNECTED) and the permission prerequisite. For a single-parameter mutation tool, an agent has everything needed to call it correctly.

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 100% and the sole parameter is already documented as 'a concrete list id already resolved via search_ma_lists. Never invent or guess one.' The description's 'resolved list_id from search_ma_lists' restates that guidance, so it adds little beyond what structured data already provides. Baseline 3 applies.

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: 'Set the account's default marketing-automation destination list'. The description makes the object concrete enough to separate from get_default_ma_list (read) and clear_default_ma_list (unset) without consulting their schemas.

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?

Clearly explains that the list_id must come from a prior search_ma_lists resolution and clarifies the scope of effect ('newly created campaign channels; existing channels retain their captured values'). However, it never mentions clear_default_ma_list as the way to unset the default, even though that sibling exists, leaving the inverse operation to inference.

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