mkdir seo-analyzer && cd seo-analyzer
npm init -y
npm install express axios cheerio openai dotenv

# .env
OPENAI_API_KEY=sk-your-key-here
PORT=3000

// src/services/seoService.js
import axios from 'axios';
import * as cheerio from 'cheerio';
import OpenAI from 'openai';

const openai = new OpenAI({ apiKey: process.env.OPENAI_API_KEY });

async function fetchPage(url) {
  const { data, headers } = await axios.get(url, {
    timeout: 15_000,
    headers: { 'User-Agent': 'Mozilla/5.0 (compatible; SEOBot/1.0)' },
    maxRedirects: 5,
  });
  return { html: data, contentType: headers['content-type'] || '' };
}

function extractSEOSignals(url, html) {
  const $ = cheerio.load(html);

  const title = $('title').first().text().trim();
  const metaDescription = $('meta[name="description"]').attr('content') || '';
  const h1 = $('h1').first().text().trim();
  const h2s = $('h2').map((_, el) => $(el).text().trim()).get();
  const h3s = $('h3').map((_, el) => $(el).text().trim()).get();
  const bodyText = $('body').text().replace(/\s+/g, ' ').trim();
  const wordCount = bodyText.split(/\s+/).length;
  const imgAltMissing = $('img').filter((_, el) => !$(el).attr('alt')).length;
  const imgTotal = $('img').length;
  const internalLinks = $('a[href]').filter((_, el) => {
    const href = $(el).attr('href') || '';
    return href.startsWith('/') || href.includes(new URL(url).hostname);
  }).length;
  const externalLinks = $('a[href]').filter((_, el) => {
    const href = $(el).attr('href') || '';
    return href.startsWith('http') && !href.includes(new URL(url).hostname);
  }).length;
  const hasJsonLd = $('script[type="application/ld+json"]').length > 0;
  const canonical = $('link[rel="canonical"]').attr('href') || null;
  const robotsMeta = $('meta[name="robots"]').attr('content') || null;

  return {
    url,
    title,
    titleLength: title.length,
    metaDescription,
    metaDescriptionLength: metaDescription.length,
    h1,
    h2Count: h2s.length,
    h3Count: h3s.length,
    h2Headings: h2s.slice(0, 5),
    wordCount,
    bodyPreview: bodyText.slice(0, 1000),
    imgTotal,
    imgAltMissing,
    internalLinks,
    externalLinks,
    hasStructuredData: hasJsonLd,
    canonical,
    robotsMeta,
  };
}

export async function analyzeSEO(url, targetKeyword = null) {
  const { html } = await fetchPage(url);
  const signals = extractSEOSignals(url, html);

  const keywordContext = targetKeyword ? `Target keyword: "${targetKeyword}"` : 'No specific target keyword provided — analyze general SEO quality.';

  const response = await openai.chat.completions.create({
    model: 'gpt-4o',
    messages: [
      {
        role: 'system',
        content: `You are a senior SEO specialist. Analyze the on-page SEO signals and provide a detailed audit.
${keywordContext}
Return ONLY a JSON object — no markdown:
{
  "overallScore": 0-100,
  "grade": "A | B | C | D | F",
  "summary": "2-3 sentence executive summary",
  "strengths": ["list of what is done well"],
  "issues": [
    {
      "issue": "string — specific problem",
      "impact": "high | medium | low",
      "currentState": "string",
      "recommendation": "string — specific action to take",
      "exampleRewrite": "string or null — suggested new version of title/meta/heading if applicable"
    }
  ],
  "quickWins": ["top 3 things to fix immediately for the biggest SEO gain"],
  "scores": {
    "title": 0-10,
    "metaDescription": 0-10,
    "headings": 0-10,
    "content": 0-10,
    "images": 0-10,
    "links": 0-10,
    "technicalSEO": 0-10
  }
}`,
      },
      {
        role: 'user',
        content: `Page signals:\n${JSON.stringify(signals, null, 2)}`,
      },
    ],
    temperature: 0.3,
    response_format: { type: 'json_object' },
  });

  return { signals, audit: JSON.parse(response.choices[0].message.content) };
}

// src/server.js
import 'dotenv/config';
import express from 'express';
import { analyzeSEO } from './services/seoService.js';

const app = express();
app.use(express.json());

app.post('/analyze', async (req, res, next) => {
  try {
    const { url, keyword } = req.body;
    if (!url) return res.status(400).json({ error: 'url is required' });
    const result = await analyzeSEO(url, keyword);
    res.json({ success: true, ...result });
  } catch (err) { next(err); }
});

// Batch analysis
app.post('/analyze/batch', async (req, res, next) => {
  try {
    const { urls, keyword } = req.body;
    if (!urls?.length) return res.status(400).json({ error: 'urls array required' });
    const results = await Promise.allSettled(urls.map(url => analyzeSEO(url, keyword)));
    res.json({
      success: true,
      results: results.map((r, i) =>
        r.status === 'fulfilled' ? { url: urls[i], ...r.value } : { url: urls[i], error: r.reason.message }
      ),
    });
  } catch (err) { next(err); }
});

app.use((err, _req, res, _next) => res.status(500).json({ error: err.message }));
app.listen(process.env.PORT ?? 3000, () => console.log('SEO Analyzer running'));

curl -X POST http://localhost:3000/analyze \
  -H "Content-Type: application/json" \
  -d '{"url": "https://yourblog.com/article", "keyword": "nodejs tutorial"}'

{
  "audit": {
    "overallScore": 62,
    "grade": "C",
    "summary": "The page has solid content depth but suffers from a weak title tag, missing meta description, and 8 images without alt text. Fixing these three issues alone could improve rankings significantly.",
    "quickWins": [
      "Rewrite title to include 'Node.js Tutorial' within first 30 characters",
      "Add a 155-character meta description with target keyword",
      "Add alt text to all 8 images"
    ],
    "issues": [
      {
        "issue": "Title tag does not contain target keyword",
        "impact": "high",
        "currentState": "Getting Started with Backend Development",
        "recommendation": "Include 'Node.js Tutorial' near the start of the title",
        "exampleRewrite": "Node.js Tutorial: Complete Guide to Backend Development (2026)"
      },
      {
        "issue": "Meta description is missing",
        "impact": "high",
        "currentState": "No meta description found",
        "recommendation": "Write a 150-160 character description with target keyword and clear value proposition",
        "exampleRewrite": "Learn Node.js from scratch in this comprehensive tutorial. Build REST APIs, handle databases, and deploy to production — step by step with real code examples."
      }
    ]
  }
}