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

Beyond the annotations (readOnly=false, openWorld=true, destructive=false), the description adds the confirmation workflow ('confirm with the user before each call'), the auth requirement (Cotlet API key with access to this app), the human-facing side effect ('Reaches other people'), and the editability guarantee. This is rich disclosure the structured fields do not carry.

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?

The opening sentence restates the title ('Publish a draft at a set time, on the web and by email') and the next sentence re-explains the same thing with the send_email detail, creating redundancy. The information is front-loaded, but a sentence of restatement costs it.

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 3-parameter mutation tool with no output schema, it covers the important behavioral facts (confirmation, auth, future-time constraint, editability). It is close to complete; only an explicit pointer to the alternative publish tool is missing.

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, but the description adds meaning: publish_at must be a future time and send_email defaults to true, delivering to subscribers unless explicitly disabled. It goes beyond the schema's field definitions.

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?

The description names a specific verb and resource ('Schedules a draft to go live at the time you set') and clearly separates this scheduling behavior from immediate publishing, implicitly distinguishing it from the sibling substack_publish_post. An agent can tell this tool schedules for a future time rather than publishing now.

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 gives clear operating context: the time must be in the future, the post stays editable until it goes out, and each call requires user confirmation by default. It does not, however, explicitly name publish_post or other alternatives and state when to prefer this one over them.

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