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Diven Rastdus
Diven Rastdus

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I Built an AI SEO Blog Writer That Reads Your Website First

#ai #seo #nextjs #webdev

Every business needs blog content for SEO. Most use one of two approaches:

  1. Pay agencies $300-500 per post and wait 2 weeks
  2. Use ChatGPT and get generic content that doesn't match their brand

I built a third option: Blogmatic -- an AI tool that actually reads your website before writing.

The Problem with Generic AI Writing

When you tell ChatGPT "write a blog post about marketing," it produces the same output whether you're a law firm, a SaaS company, or a bakery. There's no brand awareness, no industry context, no understanding of what you've already written about.

How Blogmatic Works

  1. Paste your URL -- that's it, just your website address
  2. Site analysis -- Blogmatic crawls your site using Cheerio, extracting headings, paragraphs, meta descriptions, and internal links
  3. Industry detection -- keyword frequency analysis across 10 industry categories (SaaS, e-commerce, healthcare, finance, etc.)
  4. Tone detection -- analyzes word patterns to determine if your site is formal, conversational, or professional
  5. Keyword extraction -- identifies your top keywords by frequency, filtering stop words
  6. AI generation -- Gemini 2.5 Flash generates a structured blog post using all this context

The output: a 1500-2000 word post with proper title (50-60 chars), meta description (150-155 chars), 5-7 H2 sections, natural keyword density, and a FAQ section ready for schema markup.

The Tech Stack

  • Next.js 14 with App Router and server components
  • Supabase for auth (email + Google SSO), Postgres database with Row Level Security
  • Gemini 2.5 Flash -- fast, cheap, surprisingly good at structured output with responseMimeType: 'application/json'
  • Cheerio for HTML parsing (lightweight, no headless browser needed)
  • Stripe for subscriptions (checkout sessions + webhooks)
  • Vitest for testing (28 tests covering analyzer, API routes, Stripe config)
  • Vercel for hosting

Key Technical Decision: Structured JSON Output

Instead of parsing free-form AI text, I use Gemini's responseMimeType: 'application/json' to force structured output:

const response = await ai.models.generateContent({
  model: 'gemini-2.5-flash',
  contents: prompt,
  config: {
    responseMimeType: 'application/json',
  },
})
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This returns clean JSON every time -- no regex parsing, no markdown stripping, no "sometimes it wraps in code fences" issues.

The Site Analyzer

The analyzer is surprisingly simple but effective:

const INDUSTRY_KEYWORDS: Record<string, string[]> = {
  'saas': ['software', 'platform', 'dashboard', 'api', 'integration'],
  'e-commerce': ['shop', 'buy', 'cart', 'product', 'price'],
  // ... 10 industries
}

function detectIndustry(text: string): string {
  let bestMatch = 'general'
  let bestScore = 0
  for (const [industry, keywords] of Object.entries(INDUSTRY_KEYWORDS)) {
    const score = keywords.filter(kw => text.includes(kw)).length
    if (score > bestScore) { bestScore = score; bestMatch = industry }
  }
  return bestMatch
}
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No ML model needed. Simple keyword frequency matching across pre-defined industry vocabularies. Works well enough for content generation context.

Try It

Blogmatic is live and free to try (3 posts/month, no credit card):

https://blogmatic.vercel.app

GitHub: https://github.com/astraedus/blogmatic

I'd love feedback -- especially from anyone doing content marketing. What's missing?

If you're building AI agents for production, check out my book Production AI Agents on Amazon Kindle. It covers architecture patterns, tool design, multi-agent coordination, and deployment strategies.

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