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substack-mcp

by thenavidm
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TypeScript
Hybrid

Publish a Note

publish_note
Destructive

Publishes a Substack Note live and public instantly; no drafts or preview. Requires confirm: true and supports markdown for bold, italic, and links.

Instructions

Publish a Substack Note. Notes have no draft state, so this is live and public the moment it runs, with no preview and no undo from this server. Refuses to run without confirm: true. Supports bold, italic and links through markdown.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
textYesThe Note's text. Markdown for bold, italic and links.
confirmNoSet true only when the user asked for exactly this action.
publicationNoWhich connected publication to act on, matched loosely against its hostname (for example 'example.substack.com' or just 'example'). Defaults to the first connected publication.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed3 schema fields changedv3.0.1
    • removedInput schema / $schema
      Removed value: -"http://json-schema.org/draft-07/schema#"
    • removedInput schema / additionalProperties
      Removed value: -false
    • changedInput schema / properties / confirm / description
      Previous value: -"Must be true for this to run. This action cannot be undone, so it is refused without an explicit confirmation."New value: +"Set true only when the user asked for exactly this action."
  2. First observedv2.1.1

TDQS

A4/5.0
Behavior5/5

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

Annotations already declare destructiveHint=true and idempotentHint=false, and the description reinforces rather than contradicts them: no draft state, live and public immediately, no preview, no undo from this server. It further discloses a hard precondition (refuses without confirm: true) and the supported markup, none of which the annotations convey.

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?

Front-loaded with verb and resource, then the irreversible-risk warning, then the confirm precondition. Four sentences with no padding, though the final markdown sentence duplicates the text parameter's own schema description and could be dropped.

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

Completeness4/5

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

For a destructive, non-idempotent, open-world mutation with no output schema, the description covers the risks an agent most needs: irreversibility, public visibility, and the confirm requirement. It omits what a successful call returns (note id/URL) and any auth or rate-limit context, which are minor gaps.

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

Parameters4/5

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 enforcement semantics the schema only hints at: confirm is a hard gate that causes refusal, not merely a convention. Markdown formatting is restated from the text parameter description, so the gain is modest but real.

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

Purpose4/5

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

States a specific verb and resource ("Publish a Substack Note") that clearly separates it from the draft/post siblings like create_draft, publish_draft and schedule_note. It does not, however, distinguish itself from publish_note_with_link, which is the nearest neighbour and could be confused given the note that markdown links are supported here.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

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

Usage is implied rather than stated: the immutability warning and the confirm gate tell an agent when it is safe to call, and the no-draft-state note implies this is for finished content. There is no explicit routing to alternatives (publish_note_with_link for link cards, schedule_note for future posting), which is the main gap for a tool with this many siblings.

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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