Publishing Markdown to Substack from an Agent Skill

The open-source project 'publishing-kit' has introduced a new destination for automated content distribution: Substack. Because Substack lacks a formal publishing API, the tool employs a browser-based automation strategy to navigate the platform's ProseMirror-based editor. The kit converts Markdown into HTML, specifically optimized to handle Substack's unique constraints, such as the lack of native table support and specific handling of inline code links. By using a helper script injected into the browser, the agent can programmatically prepare, audit, and publish drafts while ensuring that elements like multi-line code blocks and image alt text are preserved. This development allows developers to maintain a single source of truth in Markdown and distribute content across multiple platforms, including Substack, Medium, and Dev.to, without manual reformatting. The article provides a technical walkthrough on managing Substack's draft state and automating the final publishing workflow.