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

Beyond the annotations, the description discloses important behavioral details: the reply is public to everyone who can read the post, the author receives Substack's usual notification, external comments fail, and the call involves confirmation/owner approval. These are meaningful side effects for a write operation.

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 definition is appropriately sized and front-loads the core action. There is some slight redundancy between the first two sentences, but the extra context about visibility, notifications, and approval is relevant rather than 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 two-parameter write tool with complete schema coverage and no output schema, the description covers the key side effects, visibility, error condition, notification behavior, and approval requirement. An agent has enough information to invoke 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 coverage is 100%, so both parameters are already documented in the input schema. The description does not add syntax or format details beyond the schema baseline, which is acceptable when the schema carries the parameter burden.

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 description states a specific verb and resource—replying under a comment on the user's own post—and clarifies the scope by noting that a comment elsewhere returns an error. This distinguishes it from sibling tools like reply_to_note and like_comment.

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?

It clearly establishes the usable context: the comment must be on a post of the user's publication, and comments elsewhere on Substack produce an error. It does not explicitly route the agent to sibling alternatives, but the constraint is strong enough for correct selection.

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