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

Annotations already declare non-read-only, non-idempotent, open-world, destructive; the description adds genuine value on top — public visibility scope ('visible to everyone who can read the post'), notification side effect for the author, and the error behavior for out-of-scope comments. It doesn't say whether the reply can be edited/removed afterward, which is the main remaining gap for a mutation.

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 short sentences, front-loaded with the action, then scope, then side effect. Minor redundancy between 'Reply as you' and 'under your name' but nothing wasted.

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 mutation with no output schema, the description covers identity, visibility, scope errors, and notification behavior. Only post-action reversibility/editability 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 coverage is 100%, so comment_id and body are already documented in the schema itself. The description only adds the constraint that the referenced comment must live on your publication; no format or length guidance beyond that.

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 (reply) and resource (a comment on your post), plus the identity it posts under. The scoping ('on a post of your publication', 'a comment elsewhere on Substack returns an error') cleanly separates it from siblings like reply_to_note, like_comment, or pin_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?

Clearly bounds when it applies: only comments on your own publication's posts; comments elsewhere error out. It does not explicitly name the alternative path for other cases (reply_to_note / get_conversation), so it stops short of full when-to-use routing.

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