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

Annotations declare readOnly=false, openWorld=true, destructive=false. The description adds real context beyond that: the Note is publicly visible ('reaches other people'), it requires per-call confirmation by default, and it needs the user's API key. These are genuinely useful operational traits not captured in annotations.

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 the core action and timing, then safety/key requirements. The confirmation point is repeated ('you confirm each call' and 'confirm with the user before each call'), which is mild redundancy 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?

No output schema exists, but the description covers the action, timing semantics, character limit, confirmation requirement, and auth prerequisite. An agent has what it needs to call it correctly; return-value behavior is the only unstated element.

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 the baseline is 3. The description slightly exceeds that by explaining the behavioral effect of publish_at (immediate vs queued) and by describing link_post_id as a link card, adding meaning beyond the raw field labels.

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 ('Posts a Note') and resource (Substack Notes), and clearly distinguishes a Note (short post) from a full post. An agent can tell it apart from substack_publish_post / substack_schedule_post without opening a 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?

Gives explicit conditional behavior: 'Without publish_at it goes out now; with it, the Note waits in your scheduled Notes.' It also states a confirmation workflow. It doesn't explicitly route to siblings like substack_schedule_post, but the timing condition is clear.

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