diff --git a/backend-compliance/compliance/api/agent_check/_b13_wiring.py b/backend-compliance/compliance/api/agent_check/_b13_wiring.py
new file mode 100644
index 00000000..608b4330
--- /dev/null
+++ b/backend-compliance/compliance/api/agent_check/_b13_wiring.py
@@ -0,0 +1,67 @@
+"""B13 wiring — Widerrufsbelehrung-Reachability.
+
+Hängt sich an `state["extra_findings"]` an und rendert einen
+eigenständigen V2-HTML-Block (`widerruf_reach_html`).
+"""
+
+from __future__ import annotations
+
+import html
+import logging
+
+from compliance.services.widerrufsbelehrung_reachability_check import (
+    check_widerrufsbelehrung_reachability,
+)
+
+logger = logging.getLogger(__name__)
+
+
+def run_b13(state: dict) -> None:
+    new = check_widerrufsbelehrung_reachability(state)
+    if not new:
+        return
+    extras = state.get("extra_findings") or []
+    extras.extend(new)
+    state["extra_findings"] = extras
+    state["widerruf_reach_html"] = _render(new)
+    logger.info("B13 widerruf-reach: %d finding(s)", len(new))
+
+
+def _render(findings: list[dict]) -> str:
+    cards = []
+    for f in findings:
+        sev = (f.get("severity") or "").upper()
+        color = "#dc2626" if sev == "HIGH" else "#f59e0b"
+        scope_tag = f.get("b2c_scope") or ""
+        scope_html = (
+            f"<span style='display:inline-block;background:#fef3c7;"
+            f"color:#92400e;font-size:10px;padding:1px 6px;border-radius:999px;"
+            f"margin-left:6px;'>Scope: {html.escape(scope_tag)}</span>"
+            if scope_tag else ""
+        )
+        cards.append(
+            f"<div style='margin:12px 0;padding:14px;background:#fff;"
+            f"border-left:3px solid {color};border-radius:4px;'>"
+            f"<div style='font-weight:600;color:{color};font-size:14px;'>"
+            f"{sev} · {html.escape(f.get('check_id') or '')}{scope_html}</div>"
+            f"<div style='font-size:14px;margin-top:4px;'>"
+            f"<strong>{html.escape(f.get('title') or '')}</strong></div>"
+            f"<div style='font-size:12px;color:#64748b;margin-top:2px;'>"
+            f"{html.escape(f.get('norm') or '')}</div>"
+            f"<div style='font-size:12px;color:#475569;margin-top:6px;'>"
+            f"<em>{html.escape(f.get('evidence') or '')}</em></div>"
+            f"<div style='font-size:13px;margin-top:8px;background:#dcfce7;"
+            f"padding:8px 10px;border-radius:4px;'>"
+            f"<strong>→ Empfehlung:</strong> "
+            f"{html.escape(f.get('action') or '')}</div>"
+            "</div>"
+        )
+    return (
+        "<div style='margin:24px 0;padding:16px;border-left:4px solid #dc2626;"
+        "background:#fef2f2;border-radius:4px;'>"
+        "<h2 style='margin:0 0 8px;color:#7f1d1d;font-size:16px;'>"
+        "📜 Widerrufsbelehrung-Reachability (B2C-Pflicht)"
+        "</h2>"
+        + "".join(cards) +
+        "</div>"
+    )
diff --git a/backend-compliance/compliance/api/agent_check/_orchestrator.py b/backend-compliance/compliance/api/agent_check/_orchestrator.py
index 653e8553..bdde8681 100644
--- a/backend-compliance/compliance/api/agent_check/_orchestrator.py
+++ b/backend-compliance/compliance/api/agent_check/_orchestrator.py
@@ -23,6 +23,7 @@ from ._b5_wiring import run_b5
 from ._b6b7b8_wiring import run_b6b7b8
 from ._b9b10_wiring import run_b9b10
 from ._b12_wiring import run_b12
+from ._b13_wiring import run_b13
 from ._constants import _compliance_check_jobs
 from ._phase_a_resolve import run_phase_a
 from ._phase_b_profile_check import run_phase_b
@@ -70,6 +71,7 @@ async def run_compliance_check(check_id: str, req) -> None:
         run_b6b7b8(state)  # DPO-cross-doc + Doc-Staleness + CMP-fingerprint
         run_b9b10(state)  # Multi-Entity-Impressum + Drittland-Mechanismus
         run_b12(state)  # Chatbot-Cookie-Klassifikation (B11 ist in B9B10)
+        run_b13(state)  # Widerrufsbelehrung-Reachability (B2C-Pflicht)
         # Phase D-3 top/mid/bot: Step 5 HTML blocks
         await run_phase_d3_top(state)
         await run_phase_d3_mid(state)
diff --git a/backend-compliance/compliance/services/mail_render_v2/_compose.py b/backend-compliance/compliance/services/mail_render_v2/_compose.py
index 3afe3c4a..ca1a2d62 100644
--- a/backend-compliance/compliance/services/mail_render_v2/_compose.py
+++ b/backend-compliance/compliance/services/mail_render_v2/_compose.py
@@ -48,6 +48,8 @@ def compose_v2(state: dict) -> str:
         state.get("extra_findings_html", ""),
         # B12 Chatbot-Cookie-Klassifikation
         state.get("chatbot_cookie_html", ""),
+        # B13 Widerrufsbelehrung-Reachability (B2C-Pflicht)
+        state.get("widerruf_reach_html", ""),
         # Browser-Matrix (Stage 1.c)
         state.get("browser_matrix_html", ""),
         # All legacy build_*_html() wrapped in V2 sections — preserves
diff --git a/backend-compliance/compliance/services/widerrufsbelehrung_reachability_check.py b/backend-compliance/compliance/services/widerrufsbelehrung_reachability_check.py
new file mode 100644
index 00000000..9c04c258
--- /dev/null
+++ b/backend-compliance/compliance/services/widerrufsbelehrung_reachability_check.py
@@ -0,0 +1,183 @@
+"""B13 — Widerrufsbelehrung-Reachability-Check.
+
+Erkennt: B2C-Shop ohne öffentlich erreichbare Widerrufsbelehrung.
+
+Norm: Art. 246a § 1 Abs. 2 Nr. 1 EGBGB i.V.m. § 312d BGB —
+Widerrufsbelehrung muss dauerhaft + leicht zugänglich auf der Website
+verfügbar sein. Footer ohne Widerruf-Link + alle Widerruf-Pfade 404
+verletzt das.
+
+Signale aus state:
+  - doc_entries: ein entry mit doc_type='widerruf'. Discovery hat es
+    versucht (discovery_attempted=True), aber Text ist leer / unter
+    Mindestlänge → Pfad nicht erreichbar.
+  - DSE / Homepage / sonstige Texte: B2C-Scope-Detection per Keywords.
+
+Ein einzelnes Finding mit Schweregrad HIGH bei B2C, MEDIUM bei
+unklarem Scope, kein Finding bei klarem B2B.
+"""
+
+from __future__ import annotations
+
+import logging
+import re
+
+logger = logging.getLogger(__name__)
+
+
+# Min characters that count as 'reachable' widerruf doc.
+_MIN_TEXT_CHARS = 400
+
+
+# Strong B2C-Shop signals (Endkunden-Verkauf / E-Commerce).
+_B2C_STRONG = (
+    "warenkorb", "in den warenkorb", "zur kasse", "kasse",
+    "bestellung aufgeben", "jetzt kaufen", "preis inkl. mwst",
+    "preis inkl. mehrwertsteuer", "lieferzeit", "versandkosten",
+    "rückgaberecht", "rueckgaberecht", "rücksende",
+    "endkunden", "endverbraucher", "verbraucher i.s.d. § 13 bgb",
+)
+
+# Weaker B2C signals — only count when paired with a strong one or
+# when AT LEAST TWO appear together.
+_B2C_WEAK = (
+    "shop", "store", "kaufen", "produkt", "ware", "rechnung",
+    "agb", "widerrufsfrist", "widerrufsrecht", "wallbox", "hardware",
+    "abonnement", "tarif buchen", "naturstrom", "ladetarif",
+)
+
+# Hard B2B-only signals that override B2C-Verdacht.
+_B2B_ONLY = (
+    "ausschließlich an unternehmer", "ausschliesslich an unternehmer",
+    "nur für unternehmen", "b2b only", "kein verkauf an verbraucher",
+    "ausschluss verbraucher",
+)
+
+
+def _detect_b2c_scope(state: dict) -> tuple[str, list[str]]:
+    """Return (scope, signals_found).
+
+    scope ∈ {'b2c_strong', 'b2c_likely', 'b2b_only', 'unknown'}
+    """
+    haystack_parts: list[str] = []
+    for e in (state.get("doc_entries") or []):
+        t = (e.get("text") or "").lower()
+        if t:
+            haystack_parts.append(t)
+    home = (state.get("home_text") or "").lower()
+    if home:
+        haystack_parts.append(home)
+    hay = "\n".join(haystack_parts)
+
+    if not hay:
+        return "unknown", []
+
+    b2b_hits = [s for s in _B2B_ONLY if s in hay]
+    if b2b_hits:
+        return "b2b_only", b2b_hits
+
+    strong_hits = [s for s in _B2C_STRONG if s in hay]
+    if strong_hits:
+        return "b2c_strong", strong_hits
+
+    weak_hits = [s for s in _B2C_WEAK if s in hay]
+    if len(weak_hits) >= 2:
+        return "b2c_likely", weak_hits[:5]
+    return "unknown", weak_hits[:3]
+
+
+def _footer_has_widerruf_link(state: dict) -> bool:
+    """Best-effort scan for a Widerruf-link in footer / discovered URLs.
+
+    The discovery phase merges any same-owner widerruf URLs it finds
+    into doc_entries[widerruf].url. If that URL exists AND the
+    discovered text is non-empty, the page is reachable.
+    """
+    for e in (state.get("doc_entries") or []):
+        if e.get("doc_type") != "widerruf":
+            continue
+        url = (e.get("url") or "").strip()
+        text = (e.get("text") or "").strip()
+        if url and len(text) >= _MIN_TEXT_CHARS:
+            return True
+    # Optional: scan a raw footer-snapshot if the orchestrator stored one.
+    footer = (state.get("footer_html") or "") + " " + \
+             (state.get("footer_text") or "")
+    if footer and re.search(
+        r"widerruf|cancellation|withdrawal|rückgabe|rueckgabe",
+        footer, re.IGNORECASE,
+    ):
+        return True
+    return False
+
+
+def check_widerrufsbelehrung_reachability(state: dict) -> list[dict]:
+    """Emit a single finding when a B2C-Shop has no reachable Widerruf
+    document and no footer link to one."""
+    widerruf_entry = next(
+        (e for e in (state.get("doc_entries") or [])
+         if e.get("doc_type") == "widerruf"),
+        None,
+    )
+    if not widerruf_entry:
+        # No widerruf processing happened at all → don't fabricate.
+        return []
+
+    discovery_tried = bool(widerruf_entry.get("discovery_attempted"))
+    text_len = len((widerruf_entry.get("text") or "").strip())
+    has_url = bool((widerruf_entry.get("url") or "").strip())
+
+    if text_len >= _MIN_TEXT_CHARS:
+        # widerruf doc is actually reachable — no finding.
+        return []
+
+    if not discovery_tried and not has_url:
+        # User did not submit a widerruf URL and discovery did not run
+        # (e.g. no homepage to crawl). Cannot make a claim.
+        return []
+
+    if _footer_has_widerruf_link(state):
+        return []
+
+    scope, signals = _detect_b2c_scope(state)
+    if scope == "b2b_only":
+        return []
+
+    if scope == "unknown":
+        # Without B2C-Indikatoren remain silent — false positives at
+        # pure agency / B2B sites would erode trust in the report.
+        return []
+
+    sev = "HIGH" if scope == "b2c_strong" else "MEDIUM"
+    sev_reason = "missing" if scope == "b2c_strong" else "unverifiable"
+
+    tried_url = (widerruf_entry.get("url")
+                 or widerruf_entry.get("rejected_url") or "").strip()
+    tried_hint = f" (probiert: {tried_url})" if tried_url else ""
+
+    return [{
+        "check_id": "WIDERRUF-REACH-001",
+        "severity": sev,
+        "severity_reason": sev_reason,
+        "title": (
+            "Widerrufsbelehrung nicht öffentlich erreichbar "
+            "trotz B2C-Shop-Merkmalen"
+        ),
+        "norm": (
+            "Art. 246a § 1 Abs. 2 Nr. 1 EGBGB i.V.m. § 312d BGB"
+        ),
+        "evidence": (
+            f"Discovery hat Widerruf-Pfade versucht{tried_hint} — keine "
+            f"erreichbare Belehrung gefunden. Footer enthält keinen "
+            f"Widerruf-Link. B2C-Signale: "
+            f"{', '.join(signals[:3]) if signals else 'keine direkten'}."
+        ),
+        "action": (
+            "Eigenständige Widerrufsbelehrungs-Seite (z.B. "
+            "/widerrufsbelehrung) anlegen UND im Footer dauerhaft "
+            "verlinken. Gesetzliche Musterbelehrung nach Anlage 1 zu "
+            "Art. 246a EGBGB verwenden — eigene Formulierungen sind "
+            "abmahnfähig."
+        ),
+        "b2c_scope": scope,
+    }]
diff --git a/backend-compliance/tests/test_widerrufsbelehrung_reachability_check.py b/backend-compliance/tests/test_widerrufsbelehrung_reachability_check.py
new file mode 100644
index 00000000..eebb8cb8
--- /dev/null
+++ b/backend-compliance/tests/test_widerrufsbelehrung_reachability_check.py
@@ -0,0 +1,137 @@
+"""Tests for B13 Widerrufsbelehrung-Reachability-Check."""
+
+from compliance.services.widerrufsbelehrung_reachability_check import (
+    _detect_b2c_scope,
+    check_widerrufsbelehrung_reachability,
+)
+
+
+def _state(widerruf_entry=None, home_text="", doc_entries=None,
+           footer_text=""):
+    entries = list(doc_entries or [])
+    if widerruf_entry is not None:
+        entries.append({"doc_type": "widerruf", **widerruf_entry})
+    return {
+        "doc_entries": entries,
+        "home_text": home_text,
+        "footer_text": footer_text,
+    }
+
+
+class TestDetectB2CScope:
+    def test_strong_b2c_warenkorb(self):
+        s = _state(home_text="Legen Sie das Produkt in den Warenkorb.")
+        scope, hits = _detect_b2c_scope(s)
+        assert scope == "b2c_strong"
+        assert any("warenkorb" in h for h in hits)
+
+    def test_b2b_only_overrides_b2c(self):
+        s = _state(home_text="Wir verkaufen ausschließlich an Unternehmer. "
+                             "Warenkorb für Großkunden.")
+        scope, _ = _detect_b2c_scope(s)
+        assert scope == "b2b_only"
+
+    def test_weak_signals_two_promote_to_likely(self):
+        s = _state(home_text="Unser Shop bietet Wallbox-Produkte mit "
+                             "Rechnung zur Bestellung.")
+        scope, _ = _detect_b2c_scope(s)
+        assert scope == "b2c_likely"
+
+    def test_single_weak_signal_stays_unknown(self):
+        s = _state(home_text="Wir bieten einen Shop.")
+        scope, _ = _detect_b2c_scope(s)
+        assert scope == "unknown"
+
+    def test_empty_state(self):
+        s = _state()
+        scope, _ = _detect_b2c_scope(s)
+        assert scope == "unknown"
+
+
+class TestCheck:
+    def test_no_widerruf_entry_no_finding(self):
+        out = check_widerrufsbelehrung_reachability(_state())
+        assert out == []
+
+    def test_widerruf_reachable_no_finding(self):
+        out = check_widerrufsbelehrung_reachability(_state(
+            widerruf_entry={
+                "url": "https://shop.de/widerruf",
+                "text": "Belehrung " * 100,
+                "discovery_attempted": True,
+            },
+            home_text="Warenkorb / zur Kasse.",
+        ))
+        assert out == []
+
+    def test_unreachable_plus_b2c_strong_high_finding(self):
+        out = check_widerrufsbelehrung_reachability(_state(
+            widerruf_entry={
+                "url": "", "text": "",
+                "discovery_attempted": True,
+                "rejected_url": "https://shop.de/widerruf",
+            },
+            home_text="In den Warenkorb. Lieferzeit 2 Tage. Preis inkl. MwSt.",
+        ))
+        assert len(out) == 1
+        f = out[0]
+        assert f["check_id"] == "WIDERRUF-REACH-001"
+        assert f["severity"] == "HIGH"
+        assert f["b2c_scope"] == "b2c_strong"
+        assert "Art. 246a" in f["norm"]
+        assert "shop.de/widerruf" in f["evidence"]
+
+    def test_unreachable_plus_b2c_likely_medium(self):
+        out = check_widerrufsbelehrung_reachability(_state(
+            widerruf_entry={
+                "url": "", "text": "",
+                "discovery_attempted": True,
+            },
+            home_text="Shop bietet Wallbox und Tarif buchen.",
+        ))
+        assert len(out) == 1
+        assert out[0]["severity"] == "MEDIUM"
+        assert out[0]["b2c_scope"] == "b2c_likely"
+
+    def test_unreachable_plus_b2b_only_no_finding(self):
+        out = check_widerrufsbelehrung_reachability(_state(
+            widerruf_entry={
+                "url": "", "text": "",
+                "discovery_attempted": True,
+            },
+            home_text="B2B only — kein Verkauf an Verbraucher.",
+        ))
+        assert out == []
+
+    def test_unreachable_plus_unknown_scope_no_finding(self):
+        # Pure agency / B2B-services without clear shop signals — silent.
+        out = check_widerrufsbelehrung_reachability(_state(
+            widerruf_entry={
+                "url": "", "text": "",
+                "discovery_attempted": True,
+            },
+            home_text="Wir sind eine Beratungsagentur für Mittelstand.",
+        ))
+        assert out == []
+
+    def test_discovery_not_attempted_no_finding(self):
+        # Avoid false positives when discovery had no homepage to crawl.
+        out = check_widerrufsbelehrung_reachability(_state(
+            widerruf_entry={
+                "url": "", "text": "",
+                "discovery_attempted": False,
+            },
+            home_text="In den Warenkorb. Preis inkl. MwSt.",
+        ))
+        assert out == []
+
+    def test_footer_widerruf_link_suppresses_finding(self):
+        out = check_widerrufsbelehrung_reachability(_state(
+            widerruf_entry={
+                "url": "", "text": "",
+                "discovery_attempted": True,
+            },
+            home_text="Warenkorb. Lieferzeit. Preis inkl. MwSt.",
+            footer_text='<a href="/widerruf">Widerruf</a>',
+        ))
+        assert out == []