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Substack MCP Server

Substack MCP Server

by cotletdev
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
Hybrid

Cancel scheduled post

cancel_scheduled_post
Destructive

Stops a scheduled post from publishing or emailing by removing its scheduled time, leaving the content saved as a draft for later rescheduling.

Instructions

Stop a scheduled post from going out; it stays as a draft.

Removes the scheduled time from a post, so nothing is published or emailed then; the post stays a draft with its content. Schedule it again with schedule_post. A post with no schedule returns an error.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "post_id": "<post_id>"
    },
    "name": "cancel_scheduled_post"
  }
}

Input Schema

NameRequiredDescriptionDefault
post_idYesPost ID from list_posts.

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

A4.2/5.0
Behavior4/5

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

Annotations declare destructiveHint=true, but the description usefully scopes that destruction: only the scheduled time is removed, content is preserved as a draft. The error-for-unscheduled-post line also effectively discloses the non-idempotent behavior implied by idempotentHint=false. It stops short of saying whether an already-published post can be passed in.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The lead sentence front-loads the action and the key outcome, and the remaining clauses each contribute (re-schedule path, error case). The draft-state outcome is stated twice in slightly different words, a minor redundancy.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a one-parameter tool with annotations already covering the safety profile and no output schema, the description covers the action, the resulting state, the error condition, and the recovery path. Nothing an agent needs in order to call it correctly is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

There is a single parameter with 100% schema description coverage ('Post ID from list_posts.'), so the schema already carries the semantics. The description adds no additional meaning about post_id beyond what the schema states, making the baseline 3 appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Stop a scheduled post') plus the resulting state ('it stays as a draft'), which cleanly separates it from sibling mutations like delete_post, unpublish_post, and schedule_post. An agent can pick this 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.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Names the follow-up alternative explicitly ('Schedule it again with schedule_post') and gives a precondition ('A post with no schedule returns an error'). It doesn't explicitly contrast against delete_post or unpublish_post, which are the closest confusable siblings, so it stops short of a full when-not-to-use statement.

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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