substack2eec

Convert a Substack newsletter archive into a ready-to-send Educational Email Course (EEC).

Paste a Substack URL → the app fetches public posts, uses Claude to pick the best 3–5 lessons, rewrites each one as a tight email, and exports a ZIP of Markdown files.

How it works

1. Fetch — scrapes the Substack public archive (1 req/sec, exponential backoff on 429s, paywalled posts skipped)
2. Curate — Claude picks and sequences up to 5 posts that form a coherent course arc, using tool use for structured output
3. Rewrite — Claude rewrites each post as an email lesson (subject line, preview text, 400–600 word body, key takeaway) via streaming SSE
4. Export — download a ZIP of .md files, one per lesson

Stack

• Next.js 15 (App Router, Node runtime)
• Anthropic SDK — claude-sonnet-4-6
• Cheerio for HTML extraction
• JSZip for the export bundle

Setup

cp .env.example .env.local
# add your ANTHROPIC_API_KEY
npm install
npm run dev        # http://localhost:3000

Env vars

Variable	Required	Description
ANTHROPIC_API_KEY	yes	Anthropic API key

Never use NEXT_PUBLIC_ — API keys must not reach the client.

Dev notes

• src/lib/ files all import server-only — they contain secrets
• /api/curate streams SSE; maxDuration = 180 for Vercel
• Posts are truncated to 2500 words at extraction time (MAX_POST_WORDS)
• Spike tester: npx tsx spike/extract.ts <url> [limit]