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

Annotations already declare readOnly/idempotent/non-destructive, so the bar is lower; the description still adds real substance: newest-first ordering, the concrete fields returned (text, time, likes, restacks, reply count, link), and the omission of posts and restacks. It says nothing about auth requirements or any per-page limit for next_cursor pagination.

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?

Front-loaded with purpose, then scope exclusions, then pagination, then sibling routing – a logical order with no filler. Minor redundancy: 'newest first' appears in both the first and second sentences.

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?

There is no output schema, and the description compensates by enumerating the returned fields and their ordering. Pagination, the default-user case, and the excluded content types are all covered, leaving nothing an agent needs in order to call this 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%, with both parameters documented ('Default: you' and 'next_cursor from the previous page'). The description's 'Without user it lists yours' and 'Page with next_cursor' essentially restate that, adding no syntax or handle-format detail beyond the schema's example. Baseline 3 is appropriate.

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 ('Notes posted by you or any other Substack user') plus ordering and included fields, and explicitly excludes 'Posts and restacks of posts', which is the main ambiguity an agent would have against list_posts or get_feed. It also names the sibling that consumes its output (list_note_replies), so the tool is separable without opening the schema.

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?

'Without user it lists yours' sets the default case, and 'Pass note_id to list_note_replies, like_comment or reply_to_note' routes the agent downstream. The exclusion of posts/restacks bounds scope. It lacks an explicit statement of when to prefer a different listing tool (e.g. get_feed, list_activity), so it stops short of full alternative guidance.

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