Backend Inferencer Skill

Purpose

Infer backend technologies by analyzing HTTP headers, cookies, error pages, DNS records, and repository data.

Input

Raw signals from Phase 2:

• http_signals - Server headers, X-Powered-By, cookies
• dns_signals - Service verification TXT records
• repository_signals - Dependencies, Dockerfiles
• html_signals - Generator meta tags, CMS patterns

Technology Categories

Web Servers

Technology	Detection Signals	Weight
nginx	Server: nginx, nginx error pages	35-40
Apache	Server: Apache, Apache error pages	35-40
Microsoft IIS	Server: Microsoft-IIS	40
Caddy	Server: Caddy	35
LiteSpeed	Server: LiteSpeed	35

Programming Languages

Technology	Detection Signals	Weight
Node.js	X-Powered-By: Express, connect.sid cookie	30-40
Python	X-Powered-By: gunicorn/Werkzeug, django_session cookie	30-40
PHP	X-Powered-By: PHP, PHPSESSID cookie	35-40
Ruby	_rails_session cookie, X-Request-Id	30-40
Java	JSESSIONID cookie, X-Powered-By: Servlet	35-40
Go	Custom patterns, repo analysis	25-35
.NET	ASP.NET_SessionId cookie, X-AspNet-Version	40

Backend Frameworks

Technology	Detection Signals	Implies	Weight
Express.js	X-Powered-By: Express	Node.js	40
NestJS	Nest patterns, repo analysis	Node.js, TypeScript	35
Fastify	Fastify patterns	Node.js	35
Django	csrftoken/django_session cookies	Python	40
Flask	Werkzeug server	Python	35
FastAPI	uvicorn patterns	Python	35
Rails	_rails_session cookie	Ruby	40
Laravel	laravel_session cookie, XSRF-TOKEN	PHP	40
Symfony	symfony cookie patterns	PHP	35
Spring	JSESSIONID, X-Application-Context	Java	35
ASP.NET	ASP.NET_SessionId	.NET	40

Content Management Systems

Technology	Detection Signals	Weight
WordPress	/wp-content/, /wp-admin/, generator meta	45
Drupal	X-Drupal-Cache, /sites/default/	45
Joomla	generator meta, /components/	40
Magento	/skin/frontend/, Mage patterns	40
Shopify	myshopify.com, Shopify patterns	45
Contentful	Contentful API patterns	35
Strapi	Strapi patterns	35
Ghost	Ghost generator meta	40

Databases (Indirect Signals)

Technology	Detection Signals	Weight
PostgreSQL	pg dependency, Heroku Postgres	25-30
MySQL	mysql dependency, common patterns	25-30
MongoDB	mongoose dependency, MongoDB Atlas TXT	30
Redis	redis dependency, session patterns	25-30
Elasticsearch	elasticsearch dependency	25-30
DynamoDB	AWS SDK patterns, boto3	25-30

API Technologies

Technology	Detection Signals	Weight
GraphQL	/graphql endpoint, schema patterns	35
REST	/api/v1, OpenAPI spec	25
gRPC	grpc patterns in repos	30
tRPC	tRPC patterns	30

Inference Logic

def infer_backend_technologies(signals):
    results = []

    # Web Server Detection
    server_header = signals.http_signals.get('Server', '')
    for server in SERVER_PATTERNS:
        if server.pattern.match(server_header):
            results.append({
                "name": server.name,
                "category": "Web Server",
                "version": extract_version(server_header, server.pattern),
                "signals": [{"type": "http_header", "value": f"Server: {server_header}"}],
                "total_weight": server.weight
            })

    # Language/Framework from X-Powered-By
    powered_by = signals.http_signals.get('X-Powered-By', '')
    for framework in POWERED_BY_PATTERNS:
        if framework.pattern in powered_by:
            results.append({
                "name": framework.name,
                "category": framework.category,
                "implies": framework.implies,
                "signals": [{"type": "http_header", "value": f"X-Powered-By: {powered_by}"}],
                "total_weight": framework.weight
            })

    # Cookie-based Detection
    for cookie in signals.http_signals.cookies:
        for pattern in COOKIE_PATTERNS:
            if pattern.name in cookie:
                results.append({
                    "name": pattern.tech,
                    "category": pattern.category,
                    "implies": pattern.implies,
                    "signals": [{"type": "cookie", "value": f"Cookie: {cookie}"}],
                    "total_weight": pattern.weight
                })

    # CMS Detection from HTML
    for cms in CMS_PATTERNS:
        score = 0
        evidence = []

        if cms.generator_pattern in signals.html_signals.generators:
            score += 40
            evidence.append("Generator meta tag")

        for url_pattern in cms.url_patterns:
            if url_pattern in signals.html_signals.script_urls:
                score += 20
                evidence.append(f"URL pattern: {url_pattern}")

        if score > 0:
            results.append({
                "name": cms.name,
                "category": "CMS",
                "signals": evidence,
                "total_weight": score
            })

    # Repository-based Detection
    if signals.repository_signals:
        for dep_file, deps in signals.repository_signals.dependencies.items():
            for dep in deps:
                if dep.name in DEPENDENCY_PATTERNS:
                    pattern = DEPENDENCY_PATTERNS[dep.name]
                    results.append({
                        "name": pattern.tech,
                        "category": pattern.category,
                        "version": dep.version,
                        "signals": [{"type": "dependency", "value": f"{dep.name}@{dep.version}"}],
                        "total_weight": pattern.weight
                    })

    return results

Output

{
  "skill": "backend_inferencer",
  "results": {
    "technologies": [
      {
        "name": "nginx",
        "category": "Web Server",
        "version": "1.18.0",
        "signals": [
          {
            "type": "http_header",
            "value": "Server: nginx/1.18.0",
            "source": "https://example.com",
            "weight": 40
          }
        ],
        "total_weight": 40
      },
      {
        "name": "Express.js",
        "category": "Backend Framework",
        "signals": [
          {
            "type": "http_header",
            "value": "X-Powered-By: Express",
            "source": "https://api.example.com",
            "weight": 40
          },
          {
            "type": "cookie",
            "value": "connect.sid session cookie",
            "source": "https://example.com",
            "weight": 30
          }
        ],
        "total_weight": 70,
        "implies": ["Node.js"]
      },
      {
        "name": "Node.js",
        "category": "Runtime",
        "signals": [
          {
            "type": "implied",
            "value": "Implied by Express.js detection",
            "weight": 0
          },
          {
            "type": "dependency",
            "value": "node version in package.json",
            "source": "github.com/example/repo",
            "weight": 35
          }
        ],
        "total_weight": 35
      },
      {
        "name": "PostgreSQL",
        "category": "Database",
        "signals": [
          {
            "type": "dependency",
            "value": "pg@8.11.0 in package.json",
            "source": "github.com/example/repo",
            "weight": 30
          }
        ],
        "total_weight": 30
      }
    ],
    "implied_technologies": [
      {
        "name": "Node.js",
        "implied_by": ["Express.js"],
        "confidence": "High"
      }
    ],
    "summary": {
      "web_server": "nginx",
      "runtime": "Node.js",
      "framework": "Express.js",
      "database": "PostgreSQL",
      "cms": null
    }
  }
}

Version Detection

From Headers

Server: nginx/1.18.0 → nginx 1.18.0
X-Powered-By: PHP/8.1.0 → PHP 8.1.0
X-AspNet-Version: 4.0.30319 → ASP.NET 4.x

From Dependencies

// package.json
"express": "^4.18.2" → Express.js 4.18.x

// requirements.txt
Django==4.2.1 → Django 4.2.1

// Gemfile
gem 'rails', '~> 7.0' → Rails 7.0.x

Error Handling

• Missing headers: Continue with other signals
• Ambiguous cookies: Include all possibilities
• Conflicting signals: Report both, flag for correlation phase