diff --git a/backend-compliance/compliance/services/mandatory_content_checker.py b/backend-compliance/compliance/services/mandatory_content_checker.py
new file mode 100644
index 0000000..8631c3c
--- /dev/null
+++ b/backend-compliance/compliance/services/mandatory_content_checker.py
@@ -0,0 +1,274 @@
+"""
+Mandatory Content Checker — verifies that legally required content
+is present on a website. Checks for missing documents, sections,
+and mandatory information within documents.
+
+Knows what MUST be there (not just what IS there).
+"""
+
+import logging
+import re
+from dataclasses import dataclass, field
+
+from compliance.services.dse_parser import DSESection
+
+logger = logging.getLogger(__name__)
+
+
+@dataclass
+class MandatoryFinding:
+    code: str
+    severity: str  # "HIGH", "MEDIUM", "LOW"
+    category: str  # "document_missing", "section_missing", "info_missing"
+    text: str
+    legal_ref: str
+    expected: str  # What should be there
+    suggestion: str = ""  # How to fix
+
+
+# ═══════════════════════════════════════════════════════════════
+# MANDATORY DOCUMENTS (must exist as pages/links on the website)
+# ═══════════════════════════════════════════════════════════════
+
+MANDATORY_DOCUMENTS = [
+    {
+        "id": "impressum",
+        "name": "Impressum",
+        "legal_ref": "§5 TMG, §18 MStV",
+        "patterns": [r"impressum", r"imprint", r"legal.?notice"],
+        "severity": "HIGH",
+    },
+    {
+        "id": "datenschutz",
+        "name": "Datenschutzerklaerung",
+        "legal_ref": "Art. 13/14 DSGVO",
+        "patterns": [r"datenschutz", r"privacy", r"dsgvo"],
+        "severity": "HIGH",
+    },
+    {
+        "id": "agb",
+        "name": "AGB / Nutzungsbedingungen",
+        "legal_ref": "§305 BGB (bei Vertragsschluss)",
+        "patterns": [r"agb", r"nutzungsbedingung", r"terms"],
+        "severity": "MEDIUM",
+    },
+    {
+        "id": "widerruf",
+        "name": "Widerrufsbelehrung",
+        "legal_ref": "§355 BGB, Art. 246a §1 EGBGB (nur Fernabsatz)",
+        "patterns": [r"widerruf", r"cancellation.?policy", r"right.?of.?withdrawal"],
+        "severity": "MEDIUM",
+    },
+]
+
+
+# ═══════════════════════════════════════════════════════════════
+# MANDATORY DSE SECTIONS (Art. 13 DSGVO Pflichtangaben)
+# ═══════════════════════════════════════════════════════════════
+
+MANDATORY_DSE_CONTENT = [
+    {
+        "id": "verantwortlicher",
+        "name": "Name und Kontakt des Verantwortlichen",
+        "legal_ref": "Art. 13 Abs. 1 lit. a DSGVO",
+        "keywords": ["verantwortlich", "responsible", "controller", "betreiber"],
+        "severity": "HIGH",
+    },
+    {
+        "id": "dsb_kontakt",
+        "name": "Kontaktdaten des Datenschutzbeauftragten",
+        "legal_ref": "Art. 13 Abs. 1 lit. b DSGVO",
+        "keywords": ["datenschutzbeauftragt", "data protection officer", "dsb", "dpo"],
+        "severity": "HIGH",
+    },
+    {
+        "id": "zwecke",
+        "name": "Zwecke der Datenverarbeitung",
+        "legal_ref": "Art. 13 Abs. 1 lit. c DSGVO",
+        "keywords": ["zweck", "purpose", "verarbeitungszweck"],
+        "severity": "HIGH",
+    },
+    {
+        "id": "rechtsgrundlage",
+        "name": "Rechtsgrundlagen der Verarbeitung",
+        "legal_ref": "Art. 13 Abs. 1 lit. c DSGVO",
+        "keywords": ["rechtsgrundlage", "legal basis", "art. 6", "art.6"],
+        "severity": "HIGH",
+    },
+    {
+        "id": "speicherdauer",
+        "name": "Speicherdauer / Loeschfristen",
+        "legal_ref": "Art. 13 Abs. 2 lit. a DSGVO",
+        "keywords": ["speicherdauer", "aufbewahrung", "loeschung", "loeschfrist",
+                      "storage period", "retention", "deletion"],
+        "severity": "HIGH",
+    },
+    {
+        "id": "betroffenenrechte",
+        "name": "Betroffenenrechte (Auskunft, Loeschung, etc.)",
+        "legal_ref": "Art. 13 Abs. 2 lit. b-d DSGVO",
+        "keywords": ["betroffenenrecht", "auskunft", "berichtigung", "loeschung",
+                      "einschraenkung", "widerspruch", "data subject rights",
+                      "right to access", "right to erasure"],
+        "severity": "HIGH",
+    },
+    {
+        "id": "beschwerderecht",
+        "name": "Beschwerderecht bei Aufsichtsbehoerde",
+        "legal_ref": "Art. 13 Abs. 2 lit. d DSGVO",
+        "keywords": ["aufsichtsbehoerde", "beschwerde", "supervisory authority",
+                      "datenschutzbehoerde"],
+        "severity": "MEDIUM",
+    },
+    {
+        "id": "drittlandtransfer",
+        "name": "Drittlandtransfer-Information",
+        "legal_ref": "Art. 13 Abs. 1 lit. f DSGVO",
+        "keywords": ["drittland", "drittst", "third countr", "usa", "transfer",
+                      "standardvertragsklausel", "adequacy"],
+        "severity": "MEDIUM",
+    },
+    {
+        "id": "automatisierte_entscheidung",
+        "name": "Automatisierte Entscheidungsfindung / Profiling",
+        "legal_ref": "Art. 13 Abs. 2 lit. f DSGVO",
+        "keywords": ["automatisiert", "profiling", "automated decision", "scoring"],
+        "severity": "MEDIUM",
+    },
+]
+
+
+# ═══════════════════════════════════════════════════════════════
+# MANDATORY IMPRESSUM CONTENT (§5 TMG)
+# ═══════════════════════════════════════════════════════════════
+
+MANDATORY_IMPRESSUM_CONTENT = [
+    {
+        "id": "geschaeftsfuehrer",
+        "name": "Geschaeftsfuehrer / Vertretungsberechtigter",
+        "legal_ref": "§5 Abs. 1 Nr. 1 TMG",
+        "keywords": ["geschaeftsfuehrer", "geschäftsführer", "ceo", "managing director",
+                      "vertretungsberechtig", "vorstand"],
+        "severity": "HIGH",
+    },
+    {
+        "id": "handelsregister",
+        "name": "Handelsregisternummer",
+        "legal_ref": "§5 Abs. 1 Nr. 4 TMG",
+        "keywords": ["handelsregister", "hrb", "hra", "amtsgericht", "registergericht",
+                      "commercial register"],
+        "severity": "HIGH",
+    },
+    {
+        "id": "ust_id",
+        "name": "Umsatzsteuer-Identifikationsnummer",
+        "legal_ref": "§5 Abs. 1 Nr. 6 TMG",
+        "keywords": ["ust-id", "ust.-id", "umsatzsteuer", "vat", "de\\d{9}"],
+        "severity": "MEDIUM",
+    },
+    {
+        "id": "anschrift",
+        "name": "Anschrift (Strasse, PLZ, Ort)",
+        "legal_ref": "§5 Abs. 1 Nr. 1 TMG",
+        "keywords": ["str.", "straße", "strasse", "plz", "postleitzahl"],
+        "severity": "HIGH",
+    },
+    {
+        "id": "kontakt",
+        "name": "Kontaktmoeglichkeit (Email oder Telefon)",
+        "legal_ref": "§5 Abs. 1 Nr. 2 TMG",
+        "keywords": ["@", "telefon", "phone", "e-mail", "email", "kontakt"],
+        "severity": "HIGH",
+    },
+]
+
+
+def check_mandatory_documents(
+    scanned_pages: list[str], page_status: dict[str, int],
+) -> list[MandatoryFinding]:
+    """Check if mandatory documents/pages exist on the website."""
+    findings = []
+
+    for doc in MANDATORY_DOCUMENTS:
+        found = False
+        for page in scanned_pages:
+            if any(re.search(p, page, re.IGNORECASE) for p in doc["patterns"]):
+                status = page_status.get(page, 200)
+                if status < 400:
+                    found = True
+                else:
+                    findings.append(MandatoryFinding(
+                        code=f"DOC-ERROR-{doc['id'].upper()}",
+                        severity="HIGH",
+                        category="document_error",
+                        text=f"{doc['name']} existiert aber gibt HTTP {status} zurueck (Ladefehler!)",
+                        legal_ref=doc["legal_ref"],
+                        expected=doc["name"],
+                        suggestion=f"Seite {page} ist nicht erreichbar. Pruefen ob ein Deployment-Fehler vorliegt.",
+                    ))
+                    found = True  # Exists but broken
+                break
+
+        if not found:
+            findings.append(MandatoryFinding(
+                code=f"DOC-MISSING-{doc['id'].upper()}",
+                severity=doc["severity"],
+                category="document_missing",
+                text=f"{doc['name']} nicht auf der Website gefunden ({doc['legal_ref']})",
+                legal_ref=doc["legal_ref"],
+                expected=f"Link zu {doc['name']} muss von jeder Seite erreichbar sein",
+            ))
+
+    return findings
+
+
+def check_dse_mandatory_content(
+    sections: list[DSESection], full_text: str,
+) -> list[MandatoryFinding]:
+    """Check if privacy policy contains all mandatory sections per Art. 13 DSGVO."""
+    findings = []
+    text_lower = full_text.lower()
+
+    for req in MANDATORY_DSE_CONTENT:
+        found = any(kw in text_lower for kw in req["keywords"])
+        if not found:
+            # Also check section headings
+            found = any(
+                any(kw in s.heading.lower() or kw in s.content.lower()[:200]
+                    for kw in req["keywords"])
+                for s in sections
+            )
+
+        if not found:
+            findings.append(MandatoryFinding(
+                code=f"DSE-CONTENT-{req['id'].upper()}",
+                severity=req["severity"],
+                category="section_missing",
+                text=f"Pflichtangabe fehlt: {req['name']} ({req['legal_ref']})",
+                legal_ref=req["legal_ref"],
+                expected=req["name"],
+            ))
+
+    return findings
+
+
+def check_impressum_mandatory_content(
+    impressum_text: str,
+) -> list[MandatoryFinding]:
+    """Check if Impressum contains all mandatory info per §5 TMG."""
+    findings = []
+    text_lower = impressum_text.lower()
+
+    for req in MANDATORY_IMPRESSUM_CONTENT:
+        found = any(re.search(kw, text_lower) for kw in req["keywords"])
+        if not found:
+            findings.append(MandatoryFinding(
+                code=f"IMP-CONTENT-{req['id'].upper()}",
+                severity=req["severity"],
+                category="info_missing",
+                text=f"Impressum: {req['name']} fehlt ({req['legal_ref']})",
+                legal_ref=req["legal_ref"],
+                expected=req["name"],
+            ))
+
+    return findings