How to Move Express.js Blog to Substack

Moving from Express.js to Substack means turning a blog archive into an owned email newsletter — with a public Substack home page and posts that arrive in readers’ inboxes.

Why leave Express.js for Substack?

Express blog APIs/sites require Node ops; Substack removes publishing ops.

Substack gives you hosting for posts, email delivery, paid subscriptions, and a simpler writing workflow. The missing piece for many authors is automation: Substack has no official public posting API. That is where API Substack fits.

How API Substack helps the move

API Substack is the unofficial posting API for Substack authors. After you create a Substack publication, you connect it to API Substack and republish your archive as drafts/posts — then keep shipping new issues without living in the browser editor.

• Register on API Substack and generate an API key
• Connect your Substack publication (publication URL + `substack.sid` session cookie)
• Create drafts, publish now, or schedule posts from API, CLI, or MCP
• Turn the migration queue into a repeatable newsletter workflow

In practice: export from Express.js → create Substack → connect the publication to API Substack → republish cleaned posts → keep writing as a Substack newsletter.

Step 1 — Export from Express.js

1. Export Mongo/SQL post collections to JSON.
2. Copy uploaded assets from your storage bucket/disk.
3. Export newsletter subscribers.
4. Strip app-specific shortcodes from content.

Step 2 — Create your Substack publication

1. Create a publication at Substack and choose your name/URL
2. Write About / Welcome posts so new subscribers understand the move
3. Import your subscriber CSV in Substack (where you legally have consent)
4. Optionally connect a custom domain in Substack settings

Step 3 — Connect the publication to API Substack

1. Register on API Substack and start your key
2. Set your publication URL (example: `https://yourname.substack.com`)
3. Copy the browser cookie `substack.sid` while signed into Substack (DevTools → Application → Cookies)
4. Store the API key + cookie in your CLI, HTTP client, or Substack API MCP

Step 4 — Republish Express.js posts to Substack

1. Clean each post (title, subtitle, body, images, tags)
2. Create a draft on Substack via API Substack (`create_post` / draft flows)
3. Review the draft in Substack if the piece is sensitive or heavily formatted
4. Publish or schedule — work oldest→newest or ship a “best of” first
5. Announce the move to remaining Express.js readers with the Substack URL

For non-technical authors, install the MCP into Claude, Cursor, or Codex and ask the agent to draft/publish. For developers, use the Python client / CLI or raw HTTP. See How to post to Substack via API.

Corner cases

• SSR/SPA routing will not transfer.
• Comments systems stay behind — Substack has its own comments.
• Use API Substack for scripted republishing from JSON.

• `substack.sid` expires — refresh it when you get 401/403
• API Substack does not replace Substack’s own subscriber CSV import — connect the publication, then republish content
• Image upload and Notes are not the focus of the posting API — optimize for newsletter posts
• This is unofficial and not affiliated with Substack — keep browser login as backup

After the move

Once the Express.js archive is on Substack, keep using API Substack as your publish rail: draft tomorrow’s issue, schedule the week, or let an AI agent post through MCP. Your blog becomes a Substack newsletter you actually control.