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 new behavioral context the annotations lack: cost ('$0.003 per request'), unbounded nesting depth, and the available sort behaviors. These are useful operational facts beyond structured fields.

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?

Content is front-loaded with the purpose and return shape, followed by sorting, identifier guidance and cost. It is dense but every clause carries information; only minor tightening is possible. No filler or repetition.

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 compensates by enumerating returned fields (text, author, date, likes, replies, restacks) and the nesting structure. Safety and cost are covered. For a read-only retrieval tool this is close to complete, though pagination behavior is unaddressed.

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%, so every parameter is already documented in the schema including the identifier combinations, sort_by enum and get_sentiment. The description restates the identifier trio and sort order but adds no syntax or format detail beyond the schema, 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: 'Get the full comment thread of a Substack post, nested.' The scope is unambiguous and clearly distinct from a post-details or likes tool. However, it never explicitly names which sibling (e.g. substack_post_details, substack_post_likes) it is not, so sibling differentiation is left implicit.

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 parenthetical 'provide url, post_id, or publication together with slug' tells the agent the alternative ways to identify the target, which is a form of input guidance. But there is no guidance on when to prefer this tool over adjacent ones (e.g. post_details) and no exclusions. Usage is implied by the resource name rather than stated.

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