list_subscriptionsPublications you subscribe to, with your plan and whether their emails reach you. Returns every publication your account subscribes to, as Settings > Subscriptions lists them: name, link, plan (free, paid, comp, founding or gift, as Substack names the membership) and whether you get its emails. Your own publications are left out.
| Name | Required | Description | Default |
|---|---|---|---|
No arguments | |||
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, non-destructive, and closed-world. The description adds value beyond them by promising a complete unfiltered result set ('returns every publication'), defining the field list, and disclosing the exclusion of own publications, so an agent knows the result is exhaustive with no pagination or filtering concerns.
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?
Two sentences, front-loaded with the core purpose and return fields. The second sentence partly restates the first ('every publication your account subscribes to'), a small redundancy, but the plan-type enumeration (free, paid, comp, founding, gift) and the exclusion note earn their space.
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 parameters and no output schema, the description must carry the return-value burden, and it does: it names the four returned attributes and enumerates the possible plan values. Nothing an agent needs in order to call this correctly 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?
The tool takes zero parameters, so there is no per-parameter semantics to explain; the baseline for a 0-param schema is 4. Nothing in the description misdescribes the parameter surface.
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 resource (publications the account subscribes to) and enumerates the returned fields: name, link, plan, and email-delivery status. It also explicitly contrasts with a related concept by noting that your own publications are excluded, so an agent can distinguish it from list_subscribers.
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 sets clear scope: 'every publication your account subscribes to, as Settings > Subscriptions lists them' and states the exclusion of your own publications, which functions as a when-not rule. It stops short of naming a sibling alternative (e.g., list_subscribers for the inverse direction), so routing between sibling tools is only implied.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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