Substack MCP Server

create_note

Publish short-form content as a Substack Note from markdown. Goes live immediately to your public feed; no draft or delete option.

Instructions

Create a Substack Note (short-form content). Accepts markdown text. PUBLISHES IMMEDIATELY to your public Notes feed — Notes have no draft state on Substack, and this server has no delete tools, so there is no undo from here.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`body`	Yes	Note content in markdown format

Output Schema

TableJSON Schema

Name	Required	Description	Default
`id`	Yes
`body`	No
`date`	No
`message`	Yes
`attachment_id`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedSep 8, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "additionalProperties": false,
+  "properties": {
+    "attachment_id": {
+      "$ref": "#/properties/message"
+    },
+    "body": {
+      "type": [
+        "string",
+        "null"
+      ]
+    },
+    "date": {
+      "$ref": "#/properties/body"
+    },
+    "id": {
+      "exclusiveMinimum": 0,
+      "maximum": 9007199254740991,
+      "type": "integer"
+    },
+    "message": {
+      "type": "string"
+    }
+  },
+  "required": [
+    "id",
+    "message"
+  ],
+  "type": "object"
+}

First observedv1.0.0Mar 13, 2026

TDQS

A4.5/5.0

Behavior5/5

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

Beyond the annotations, the description discloses critical behavioral traits: it PUBLISHES IMMEDIATELY, Notes have no draft state, and this server has no delete tools, making the action irreversible. This is valuable context that annotations alone do not provide.

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

Conciseness5/5

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

The description is two focused sentences: the first states the core action, and the second delivers the essential consequence (immediate, irreversible publishing). Every phrase earns its place and the key warning is front-loaded.

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 single-parameter tool with an output schema and annotations present, the description covers the essential decision factors: what it creates, that it publishes publicly, that there is no draft or undo path, and that markdown is supported. No critical calling information 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?

The input schema already fully documents the only parameter 'body' with 'Note content in markdown format'. The description adds only 'Accepts markdown text,' which does not meaningfully expand on the schema. With 100% schema coverage, a baseline of 3 is 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?

The description uses a specific verb and resource: 'Create a Substack Note (short-form content).' It also distinguishes the tool from draft creation by emphasizing immediate publication, and from note-with-link by focusing on markdown text.

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?

The description clearly conveys that this tool publishes immediately and that Notes have no draft state, so an agent can infer it is for public short-form content rather than drafts. It does not explicitly name alternatives like create_draft or create_note_with_link, but the context is strong enough to guide selection.

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