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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so safety is covered; the description adds genuinely new behavioral context: the response carries sent/failed/queued counts, whether the plan includes comment DMs (Team included, paid add-on on Creator), and a reconnect_reason field for a broken Instagram connection. That is real payoff information an agent cannot get from the structured fields, especially since no output schema exists.

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?

Two tight sentences, front-loaded with what is listed before the supporting detail about access and reconnection. The trailing 'Instagram only.' fragment is slightly abrupt but earns its place as a hard scoping constraint; there is no filler.

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 read-only, single-parameter listing tool with no output schema, the description covers what is returned, the account-type gating, and the failure mode (Instagram needing reconnection), which is close to everything an agent needs to call and interpret it. Only minor gaps remain, such as ordering or whether an empty list is distinguishable from an unconnected account.

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?

With a single parameter at 100% schema coverage, the schema already documents workspace_id as required and tells the caller to obtain one from list_workspaces. The description adds no additional meaning about the parameter (no format, no default, no alternate lookup), so the baseline of 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 ('Lists the workspace's Instagram comment DM rules') and then defines the domain concept inline ('a keyword comment sends one private DM'), which lets an agent distinguish this from create/update/delete_comment_dm_rule and from list_comment_dm_posts without opening any 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?

The 'Instagram only' constraint gives a clear applicability boundary, and the scope explanation implies this is the read/inspection entry point before creating or deleting rules. However, it never explicitly routes the agent away from the very similar sibling 'list_comment_dm_posts' or states when to use this versus those alternatives, leaving selection to inference.

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