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

Annotations only declare readOnlyHint=true, so the description carries the return-shape burden and does so well: ordering (newest first), inclusion of the parent post, and the identity distinction (known people get object_id, others only a name and Substack handle). It stops short of mentioning pagination or rate limits, but the data-shape disclosure is genuinely additive.

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 front-loaded sentences that lead with the resource and scope before detailing return content. The final known_only sentence is somewhat redundant with the schema but the overall text is dense and waste-free.

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 must convey the return shape, and it does: ordering, post context, and commenter identity fields. Parameters are covered by the schema and safety by annotations, leaving only minor gaps like whether the 'free posts' scope is fixed or a limit on result volume.

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 100%, so both parameters are already documented. The description's 'known_only keeps just the people they know' largely restates the schema's 'Only commenters already in the Brain' and adds no new syntax or format detail, 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?

States a specific verb and resource ('comments on the user's free Substack posts') and scopes it further with 'newest first' and 'with the post each is on'. This clearly separates it from siblings like get_substack_posts, get_substack_post_stats, and get_substack_subscribers, though it never names a sibling explicitly.

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 description explains what is returned but gives no when-to-use condition, no prerequisites, and no alternatives (e.g. when to reach for this vs. get_substack_posts or get_linkedin_post_comments). The agent must infer intent purely from the resource name.

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