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

Annotations already declare readOnly/non-destructive/openWorld, so the safety profile is covered. The description adds meaningful non-structured context: the reply thread is nested to any depth, quoted notes/posts are included, and there is a $0.003 per-request cost — billing being valuable operational context an agent wouldn't otherwise know.

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?

A single dense paragraph that front-loads purpose, then return contents, then the calling constraint and price. Every clause carries information, though the return-value enumeration is slightly packed.

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 carries the return-shape burden and does so thoroughly (note text, author, date, likes, replies, restacks, quoted post, nested reply thread). It also covers the calling constraint and billing, leaving nothing essential for an agent to call 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 all three parameters (url, note_id, get_sentiment) are already documented in the schema. The description reinforces the url/note_id mutual exclusivity but adds no semantics beyond the schema, making the baseline 3 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 (Get) and resource (a Substack Note) with clear scope, and the mention of 'replies' and 'quoted post' distinguishes it from sibling note/list tools like search_substack_notes. An agent can immediately tell this is a single-note detail endpoint.

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?

Gives clear context for invocation ('provide exactly one of url, note_id'), which tells the agent how the tool must be called. It doesn't explicitly contrast with alternatives like substack_post_details or search_substack_notes, but the use case (fetch one note) is unambiguous.

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