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

Annotations already declare readOnlyHint=true, openWorldHint=true and destructiveHint=false, so safety is covered. The description adds genuinely useful behavior beyond that: cursor pagination, empty attachments for text-only replies, null for missing values, and expiring media URLs. However, the cost statements contradict each other ("at least 10 Nexscope credits" vs "1 credit per request"), which is the kind of ambiguity that can mislead an agent deciding whether to retry.

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?

The description contains pasted navigation and pricing boilerplate ("Facebook Comment Replies API View Pricing Get the replies to a comment...", "Actual supplier units are reported per request. Examples are not guaranteed prices."), and states the retrieval purpose twice. Roughly half the text is merchandising noise rather than operational guidance, and it is not front-loaded around the actual call behavior.

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?

With no output schema, the description usefully characterizes the return payload (attachments array with type, id, url, preview_url, width, height) and its edge cases, which an agent otherwise could not know. What is missing is how pagination terminates and which cost figure to trust, but the essentials for calling the tool correctly are present.

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 schema already explains that feedback_id is not the comment id and that cursor paginates to the next page. The description adds no parameter-level detail beyond what structured fields provide, so the 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?

The opening sentence gives a specific verb and resource ("Get the replies to a comment") and lists concrete return content (attachments for image, GIF, video, sticker). It is clear what the tool retrieves, but it never explicitly contrasts itself with the sibling social_facebook_post_comments, leaving the comment-vs-reply split to be inferred from the name alone.

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?

There is no statement of when to use this tool versus alternatives, nor any prerequisite guidance (that feedback_id and expansion_token must first be obtained from the comments endpoint appears only in the schema). The agent must reverse-engineer the call sequence from parameter descriptions rather than from the tool description.

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