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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description still adds real value by saying "Reading the list marks nothing read" and by naming next_cursor for paging, but does not cover rate limits, ordering guarantees beyond "newest first", or empty-state behavior.

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?

Dense but front-loaded: the first sentence states what the feed is and its ordering, then successive clauses cover types, grouping, per-item fields and pagination. Nearly every clause carries information an agent needs and nothing is redundant.

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 well by describing returned fields (type, from, people, comment_id/text, on_comment_id, on_post_id) and the pagination token. What remains thin is the selection guidance against siblings, but the call itself is fully specified.

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 cursor and the filter enum (all/replies/restacks) are fully documented in structured fields. The description spends its parameter-adjacent text on the item `type` values (note_reply, follow, mention…) and on from/people fields, which are response fields rather than inputs, so it adds little direct meaning to the two actual parameters.

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?

Opens with a concrete verb and resource: the Substack notifications feed (replies, likes, followers, restacks), ordered newest first. It is clearly distinct from list_comments, get_unread_counts and list_notes by content, though it never names a sibling to contrast with.

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 implies context ("Returns the Activity tab of the Substack app") and explains paging via next_cursor, but gives no explicit when-to-use versus when-not, and does not say how this differs from get_unread_counts or list_comments when an agent wants reply/mention data.

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