diff --git a/app/api/shape/route.ts b/app/api/shape/route.ts
index 25c392a..e4f7dec 100644
--- a/app/api/shape/route.ts
+++ b/app/api/shape/route.ts
@@ -1,11 +1,14 @@
 import { NextRequest, NextResponse } from "next/server";
 import { shape } from "@/lib/shape";
+import { reportShapeError } from "@/lib/monitoring";
 import type { ShapeEngine, ShapeProfile } from "@/lib/types";
 
 const VALID_PROFILES = ["narrative_segment_v0", "concept_blob_v0"];
 const VALID_ENGINES = ["openai", "local"];
 
 export async function POST(request: NextRequest) {
+  let engineForReport: ShapeEngine | "unknown" = "unknown";
+  let profileForReport: ShapeProfile | "unknown" | "default" = "unknown";
   try {
     const body = await request.json();
     const text = body?.text;
@@ -27,11 +30,17 @@ export async function POST(request: NextRequest) {
       engine && VALID_ENGINES.includes(engine)
         ? (engine as ShapeEngine)
         : "openai";
+    engineForReport = engineOverride;
+    profileForReport = profileOverride ?? "default";
 
     const result = await shape(text, profileOverride, engineOverride);
     return NextResponse.json(result);
   } catch (err: unknown) {
     const message = err instanceof Error ? err.message : "Unknown error";
+    await reportShapeError(err, "POST /api/shape", {
+      engine: engineForReport,
+      profile: profileForReport,
+    });
     return NextResponse.json({ error: message }, { status: 500 });
   }
 }
diff --git a/lib/engine.ts b/lib/engine.ts
index b0f769e..bd940ec 100644
--- a/lib/engine.ts
+++ b/lib/engine.ts
@@ -1,6 +1,7 @@
 import { buildSystemPrompt } from "./prompt";
 import { runLocalShape } from "./local-engine";
 import { runOpenAIShapePrompt } from "./model";
+import { reportShapeError } from "./monitoring";
 import type { ShapeEngine, ShapeProfile } from "./types";
 
 export async function runShapeEngine({
@@ -21,7 +22,12 @@ export async function runShapeEngine({
 
   try {
     return JSON.parse(raw);
-  } catch {
+  } catch (err) {
+    await reportShapeError(err, "runShapeEngine.parseModelJson", {
+      engine,
+      profile,
+      raw_preview: raw.slice(0, 200),
+    });
     throw new Error("Model returned invalid JSON");
   }
 }
diff --git a/lib/monitoring.ts b/lib/monitoring.ts
new file mode 100644
index 0000000..b16a67f
--- /dev/null
+++ b/lib/monitoring.ts
@@ -0,0 +1,68 @@
+// Production error monitoring for Shape's critical paths.
+//
+// When SHAPE_MONITORING_DSN is configured, server-side errors in the
+// Shape API route and engine are reported to the monitoring backend
+// (Sentry-compatible payload). When the DSN is unset, this module
+// is a no-op so local development and unauthenticated previews don't
+// emit telemetry.
+//
+// Use reportShapeError(err, context, extra?) at every catch site that
+// sits on a request path. Without it, model failures, JSON parse
+// errors, and provider outages disappear into a 500 with no alerting.
+
+const DSN = process.env.SHAPE_MONITORING_DSN || "";
+const RELEASE = process.env.SHAPE_RELEASE || "dev";
+const ENVIRONMENT = process.env.SHAPE_ENVIRONMENT || process.env.NODE_ENV || "unknown";
+
+export function isMonitoringEnabled(): boolean {
+  return DSN !== "";
+}
+
+export interface ShapeErrorContext {
+  context: string;
+  release: string;
+  environment: string;
+  message: string;
+  stack?: string;
+  timestamp: string;
+  [key: string]: unknown;
+}
+
+/**
+ * Send a structured error report to the monitoring backend.
+ *
+ * Fire-and-forget. Failures inside the monitor itself MUST NOT crash the
+ * caller — a request path that depends on its own alerting being healthy
+ * is its own outage source.
+ */
+export async function reportShapeError(
+  error: unknown,
+  context: string,
+  additionalData?: Record<string, unknown>,
+): Promise<void> {
+  if (!isMonitoringEnabled()) {
+    return;
+  }
+  const payload: ShapeErrorContext = {
+    context,
+    release: RELEASE,
+    environment: ENVIRONMENT,
+    message: error instanceof Error ? error.message : String(error),
+    stack: error instanceof Error ? error.stack : undefined,
+    timestamp: new Date().toISOString(),
+    ...(additionalData ?? {}),
+  };
+  try {
+    await fetch(DSN, {
+      method: "POST",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify(payload),
+      keepalive: true,
+    });
+  } catch {
+    // Monitoring egress failures should not break the request path.
+    // The local console line below survives regardless of DSN state
+    // so a developer tailing logs still sees the original error.
+    console.error(`[shape:monitor:dropped] ${context}:`, error);
+  }
+}