diff --git a/src/app/api/quota/preview/route.ts b/src/app/api/quota/preview/route.ts
new file mode 100644
index 0000000000..242289fdbf
--- /dev/null
+++ b/src/app/api/quota/preview/route.ts
@@ -0,0 +1,78 @@
+/**
+ * GET /api/quota/preview — dry-run quota enforcement check
+ *
+ * Resolves the pool/connection for the given apiKeyId + poolId, then calls
+ * enforceQuotaShare() with the estimated cost WITHOUT consuming any counters.
+ * The enforceQuotaShare function is itself a read-only "peek" operation on the
+ * hot path — it does not call store.consume(), only store.peek().
+ *
+ * Query params (Zod: QuotaPreviewQuerySchema):
+ *   - apiKeyId: string (required)
+ *   - poolId: string (required)
+ *   - estimatedTokens?: number
+ *   - estimatedUsd?: number
+ *   - estimatedRequests?: number
+ *
+ * Response: { decision: EnforceDecision }
+ *
+ * Auth: requireManagementAuth
+ * Sanitization: all error responses via buildErrorBody (Hard Rule #12, B25)
+ *
+ * Part of: Group B — REST routes for Quota Sharing (plan 22, frente F8).
+ */
+
+import { NextResponse } from "next/server";
+import { buildErrorBody } from "@omniroute/open-sse/utils/error";
+import { requireManagementAuth } from "@/lib/api/requireManagementAuth";
+import { QuotaPreviewQuerySchema } from "@/shared/schemas/quota";
+import { getPool } from "@/lib/localDb";
+import { enforceQuotaShare } from "@/lib/quota/enforce";
+
+export const dynamic = "force-dynamic";
+
+export async function GET(request: Request): Promise<Response> {
+  const authError = await requireManagementAuth(request);
+  if (authError) return authError;
+
+  try {
+    const { searchParams } = new URL(request.url);
+
+    // Parse and validate query params
+    const parsed = QuotaPreviewQuerySchema.safeParse({
+      apiKeyId: searchParams.get("apiKeyId") ?? undefined,
+      poolId: searchParams.get("poolId") ?? undefined,
+      estimatedTokens: searchParams.get("estimatedTokens") ?? undefined,
+      estimatedUsd: searchParams.get("estimatedUsd") ?? undefined,
+      estimatedRequests: searchParams.get("estimatedRequests") ?? undefined,
+    });
+
+    if (!parsed.success) {
+      return NextResponse.json(buildErrorBody(400, parsed.error.message), { status: 400 });
+    }
+
+    const { apiKeyId, poolId, estimatedTokens, estimatedUsd, estimatedRequests } = parsed.data;
+
+    // Resolve pool to get connectionId and provider
+    const pool = getPool(poolId);
+    if (!pool) {
+      return NextResponse.json(buildErrorBody(404, "Pool not found"), { status: 404 });
+    }
+
+    // Dry-run enforcement — enforceQuotaShare only peeks (does not consume)
+    const decision = await enforceQuotaShare({
+      apiKeyId,
+      connectionId: pool.connectionId,
+      provider: "", // Unknown at this level; planResolver will handle catalog/empty fallback
+      estimatedCost: {
+        tokens: estimatedTokens,
+        usd: estimatedUsd,
+        requests: estimatedRequests,
+      },
+    });
+
+    return NextResponse.json({ decision });
+  } catch (err) {
+    const message = err instanceof Error ? err.message : "Failed to preview quota enforcement";
+    return NextResponse.json(buildErrorBody(500, message), { status: 500 });
+  }
+}