Newsletter AI Agent
Your newsletter written, published, and sent while you sleep
Dual-channel system that publishes to Substack and sends via Resend Broadcasts. Generates content, scores subjects, structures 13 HTML sections, and schedules Thursday sends. Fully automatic.
13+
Newsletters sent
weekly Thursday cadence
2
Distribution channels
Substack + Resend Broadcasts
13
Sections per newsletter
custom HTML template
The Challenge
Writing a consistent weekly newsletter requires hours of curation, writing, and formatting. Most creators give up before month 3.
The Approach
Agent that automatically curates content, generates AI summaries, scores subjects to maximize opens, and publishes to two channels: Substack (reverse-engineered API, Markdown→Tiptap JSON, auto-tagging) and Resend Broadcasts (13-section HTML template).
Architecture
Substack API reverse-engineering: Markdown→Tiptap JSON conversion for direct publishing
Subject line scoring with Claude Haiku: evaluates clarity, urgency, and relevance
Responsive 13-section HTML template adapted for email clients
Weekly stats integration: site metrics automatically included
Dry-run mode: generates and previews without sending for manual review
Key Technical Decisions
Claude Haiku 4.5 for generation: minimal cost for curated, not creative content
Reverse-engineered Substack API vs. email only: maximizes organic discoverability
Resend Broadcasts as parallel channel: full control over format and analytics
Thursday cadence: industry data indicates best B2B open rates
How It Was Built
The agent publishes to two channels simultaneously. For Substack, reverse-engineered the undocumented API: converts Markdown to Tiptap JSON (Substack internal format), applies content-based auto-tagging, and schedules publishing. For Resend Broadcasts, generates a 13-section HTML template (hero, news, tips, tools, site metrics, etc.) and schedules delivery. Subject scoring uses Claude Haiku to evaluate multiple candidates and select the one with highest open potential.
Results
From concept to 13+ weekly editions without missing a beat. The dual system maximizes reach: Substack for organic discoverability and subscriber growth, Resend Broadcasts for full format control and advanced analytics. Weekly Thursday cadence maintains consistent engagement.
Tech Stack
What you get
- Dual publishing: Substack + direct email via Resend Broadcasts
- Automatic curation of relevant industry content
- AI subject line scoring to maximize open rates
- 13-section HTML template: hero, news, tips, tools, and more
- Thursday cadence - the optimal day for B2B newsletters
- Dry-run mode to review before sending