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substack-mcp

by thenavidm
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TypeScript
Hybrid

Publish a Note with a link card

publish_note_with_link
Destructive

Publish a Note with an attached link that renders as a preview card. Requires confirm: true because it goes live publicly immediately.

Instructions

Publish a Note with a link attached, which renders as a preview card rather than a bare URL. Live and public immediately, so it refuses to run without confirm: true.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
urlYesThe URL to attach as a card.
textYesThe Note's text, shown above the card.
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

A4.2/5.0
Behavior4/5

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

Annotations already declare readOnlyHint=false, destructiveHint=true, idempotentHint=false and openWorldHint=true, so the safety profile is covered. The description adds genuinely new context: the post goes live and public immediately and a confirm gate is enforced, which tells the agent this is an irreversible outward-facing action. It stops short of describing failure modes or partial-success behavior.

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?

Two tight sentences, zero filler, and the most decision-relevant fact (immediate public permanence) is placed before the confirm requirement.

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 4-parameter mutation tool with no output schema, the description covers intent, the visibility consequence, and the mandatory confirmation. Minor gaps remain around error behavior and what the tool returns on success, but nothing required 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?

Schema description coverage is 100%, so url, text, confirm and publication are already fully documented in the schema, which sets the baseline at 3. The description reinforces the confirm parameter's gating role but adds no format, matching rules, or defaults beyond what the schema states.

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 (publish) and resource (a Note with an attached link), plus the distinguishing rendering behavior — a preview card rather than a bare URL. This implicitly separates it from the sibling publish_note, which publishes a note without a link card, so an agent can route correctly without opening either 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?

Gives a firm precondition — it refuses to run unless confirm: true — and states the consequence of calling it (live and public immediately). It does not name alternatives such as publish_note for link-free notes or schedule_note for deferred publishing, so the when-not guidance is incomplete.

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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