Claude Code for Classic ASP to Modern (2026)

Why Claude Code for Classic ASP Migration

Classic ASP (Active Server Pages) with VBScript still runs internal portals, HR systems, and reporting dashboards on Windows Server/IIS installations across thousands of organizations. These applications mix VBScript code with HTML, use ADODB recordsets for data access, and rely on server-side includes for code reuse. Microsoft ended mainstream support years ago, and each Windows Server upgrade increases the risk of breaking COM component dependencies.

Claude Code parses the interwoven VBScript/HTML, extracts ADODB connection strings and SQL queries into proper data access layers, and converts the procedural spaghetti into structured MVC or API-based architectures. It understands ASP-specific objects (Request, Response, Server, Session, Application) and maps them to modern equivalents.

The Workflow

Step 1: Analyze the Classic ASP Application

mkdir -p ~/asp-migration/{source,output}
# Inventory ASP files
find /path/to/asp-app -type f \( -name "*.asp" -o -name "*.inc" \) \
  | sort > ~/asp-migration/inventory.txt
# Count key patterns
echo "ADO connections: $(grep -rn 'ADODB.Connection' /path/to/asp-app --include='*.asp' --include='*.inc' | wc -l)"
echo "Recordsets: $(grep -rn 'ADODB.Recordset' /path/to/asp-app --include='*.asp' | wc -l)"
echo "Includes: $(grep -rn '#include' /path/to/asp-app --include='*.asp' | wc -l)"
echo "Session vars: $(grep -rn 'Session(' /path/to/asp-app --include='*.asp' | wc -l)"
echo "Inline SQL: $(grep -rn 'Execute\|CommandText' /path/to/asp-app --include='*.asp' | wc -l)"

Step 2: Convert ASP Pages to Express Routes

Original Classic ASP with inline VBScript:

<!-- #include file="includes/connection.inc" -->
<!-- #include file="includes/auth_check.inc" -->
<%
Dim rs, sql, searchTerm, pageNum, pageSize
searchTerm = Request.QueryString("q")
pageNum = CInt(Request.QueryString("page"))
If pageNum < 1 Then pageNum = 1
pageSize = 25
' SQL injection vulnerability in original code is common
sql = "SELECT TOP " & pageSize & " emp_id, first_name, last_name, " & _
      "department, hire_date, salary " & _
      "FROM employees " & _
      "WHERE (first_name LIKE '%" & searchTerm & "%' " & _
      "OR last_name LIKE '%" & searchTerm & "%') " & _
      "AND is_active = 1 " & _
      "ORDER BY last_name, first_name"
Set rs = Server.CreateObject("ADODB.Recordset")
rs.Open sql, conn
%>
<html>
<body>
<h1>Employee Search</h1>
<form method="get" action="search.asp">
  <input type="text" name="q" value="<%=Server.HTMLEncode(searchTerm)%>">
  <input type="submit" value="Search">
</form>
<table border="1">
<tr><th>Name</th><th>Department</th><th>Hire Date</th><th>Salary</th></tr>
<% Do While Not rs.EOF %>
<tr>
  <td><%=Server.HTMLEncode(rs("first_name") & " " & rs("last_name"))%></td>
  <td><%=Server.HTMLEncode(rs("department"))%></td>
  <td><%=FormatDateTime(rs("hire_date"), 2)%></td>
  <td><%=FormatCurrency(rs("salary"))%></td>
</tr>
<% rs.MoveNext
Loop
rs.Close
Set rs = Nothing
conn.Close
Set conn = Nothing %>
</table>
</body>
</html>

Claude Code generates a secure, separated Express app:

// routes/employees.js
const express = require('express');
const router = express.Router();
const { pool } = require('../db');
const { query, validationResult } = require('express-validator');
router.get('/search',
  query('q').optional().isString().trim().escape(),
  query('page').optional().isInt({ min: 1 }).toInt(),
  async (req, res, next) => {
    try {
      const errors = validationResult(req);
      if (!errors.isEmpty()) {
        return res.status(400).json({ errors: errors.array() });
      }
      const searchTerm = req.query.q || '';
      const page = req.query.page || 1;
      const pageSize = 25;
      const offset = (page - 1) * pageSize;
      // Parameterized query fixes SQL injection from original ASP
      const { rows, rowCount } = await pool.query(`
        SELECT emp_id, first_name, last_name,
               department, hire_date, salary
        FROM employees
        WHERE ($1 = '' OR first_name ILIKE $2 OR last_name ILIKE $2)
          AND is_active = true
        ORDER BY last_name, first_name
        LIMIT $3 OFFSET $4
      `, [searchTerm, `%${searchTerm}%`, pageSize, offset]);
      const countResult = await pool.query(`
        SELECT COUNT(*) as total FROM employees
        WHERE ($1 = '' OR first_name ILIKE $2 OR last_name ILIKE $2)
          AND is_active = true
      `, [searchTerm, `%${searchTerm}%`]);
      res.render('employees/search', {
        employees: rows,
        searchTerm,
        page,
        pageSize,
        totalCount: parseInt(countResult.rows[0].total),
        totalPages: Math.ceil(countResult.rows[0].total / pageSize)
      });
    } catch (err) {
      next(err);
    }
  }
);
module.exports = router;

<!-- views/employees/search.ejs -->
<h1>Employee Search</h1>
<form method="get" action="/employees/search">
  <input type="text" name="q" value="<%= searchTerm %>">
  <button type="submit">Search</button>
</form>
<table>
  <thead>
    <tr><th>Name</th><th>Department</th><th>Hire Date</th><th>Salary</th></tr>
  </thead>
  <tbody>
    <% employees.forEach(emp => { %>
    <tr>
      <td><%= emp.first_name %> <%= emp.last_name %></td>
      <td><%= emp.department %></td>
      <td><%= new Date(emp.hire_date).toLocaleDateString() %></td>
      <td><%= new Intl.NumberFormat('en-US', {style:'currency', currency:'USD'}).format(emp.salary) %></td>
    </tr>
    <% }) %>
  </tbody>
</table>

Step 3: Convert connection.inc and auth_check.inc

// db.js — replaces connection.inc
const { Pool } = require('pg');
const pool = new Pool({
  connectionString: process.env.DATABASE_URL,
  max: 20,
  idleTimeoutMillis: 30000
});
module.exports = { pool };
// middleware/auth.js — replaces auth_check.inc
function requireAuth(req, res, next) {
  if (!req.session?.userId) {
    return res.redirect('/login');
  }
  next();
}
module.exports = { requireAuth };

Step 4: Verify

cd ~/asp-migration/output
npm install express pg ejs express-session express-validator helmet
npm test
# Compare page output
curl -s "http://old-server/search.asp?q=smith" > /tmp/asp-output.html
curl -s "http://localhost:3000/employees/search?q=smith" > /tmp/node-output.html
diff <(xmllint --html --xpath '//table' /tmp/asp-output.html 2>/dev/null) \
     <(xmllint --html --xpath '//table' /tmp/node-output.html 2>/dev/null)

CLAUDE.md for Classic ASP Migration

# Classic ASP to Node.js/Express Migration Standards
## Domain Rules
- Request.QueryString maps to req.query, Request.Form maps to req.body
- Response.Write maps to res.render() with templates
- Server.HTMLEncode maps to EJS auto-escaping (<%= %>)
- Session("key") maps to req.session.key
- Application("key") maps to app.locals.key
- ADODB.Connection maps to pg Pool
- ADODB.Recordset maps to pool.query() results array
- Server.CreateObject maps to require() / npm packages
- All inline SQL must become parameterized queries
## File Patterns
- Source: *.asp, *.inc (server-side includes)
- Target: Express.js + EJS templates + PostgreSQL
- ASP pages: src/routes/ + src/views/
- INC includes: src/middleware/ or src/lib/
- Global.asa: src/app.js (startup/shutdown)
## Common Commands
- npm install express pg ejs express-session helmet
- node --watch src/app.js
- npm test
- npx eslint src/ --fix

Common Pitfalls in Classic ASP Migration

  • SQL injection everywhere: Classic ASP code routinely concatenates user input into SQL strings. Claude Code replaces every instance with parameterized queries, treating this as the highest-priority fix during migration.

  • COM object dependencies: ASP apps using Server.CreateObject for Excel, PDF generation, or email (CDO.Message) need npm package replacements. Claude Code maps CDONTS to nodemailer, Excel COM to exceljs, and FileSystemObject to Node.js fs.

  • Session affinity requirements: Classic ASP sessions are in-process and tied to a single IIS server. Claude Code adds a PostgreSQL or Redis session store to enable horizontal scaling that was impossible with the original architecture.

Frequently Asked Questions

Do I need a paid Anthropic plan to use this?

Claude Code works with any Anthropic API plan, including the free tier. However, the free tier has lower rate limits (requests per minute and tokens per minute) that may slow down multi-step workflows. For professional use, the Build or Scale plan provides higher limits and priority access during peak hours.

How does this affect token usage and cost?

The token cost depends on the size of your prompts and Claude’s responses. Typical development tasks consume 10K-50K tokens per interaction. Using a CLAUDE.md file and skills reduces exploration tokens by 50-80%, which directly lowers costs. Monitor your usage at console.anthropic.com/settings/billing.

Can I customize this for my specific project?

Yes. All Claude Code behavior can be customized through CLAUDE.md (project rules), .claude/settings.json (permissions), and .claude/skills/ (domain knowledge). The most impactful customization is adding your project’s specific patterns, conventions, and common commands to CLAUDE.md so Claude Code follows your standards from the start.

What happens when Claude Code makes a mistake?

Claude Code creates files and edits through standard filesystem operations, so all changes are visible in git diff. If a change is wrong, revert it with git checkout -- <file> for a single file or git stash for all changes. Claude Code does not make irreversible changes unless you explicitly allow destructive commands in settings.json.

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