diff --git a/StockMonitor/Utils/KoreanStockID.swift b/StockMonitor/Utils/KoreanStockID.swift
new file mode 100644
index 0000000..d2e21f3
--- /dev/null
+++ b/StockMonitor/Utils/KoreanStockID.swift
@@ -0,0 +1,32 @@
+import Foundation
+
+/// Helpers for converting between Stockbar's internal Korean stock ID
+/// (`kr_<6digit>.ks` for KOSPI, `kr_<6digit>.kq` for KOSDAQ) and Yahoo
+/// Finance symbol (`005930.KS`, `293490.KQ`).
+enum KoreanStockID {
+
+    /// Stockbar-internal ID prefix for Korean stocks.
+    static let prefix = "kr_"
+
+    /// Returns true if `id` looks like a Korean stock ID. Case-insensitive on the prefix.
+    static func isKorean(_ id: String) -> Bool {
+        let lower = id.lowercased()
+        guard lower.hasPrefix(prefix) else { return false }
+        return lower.count > prefix.count
+    }
+
+    /// Convert internal ID → Yahoo symbol. Returns nil for non-Korean IDs.
+    /// e.g. `kr_005930.ks` → `005930.KS`
+    static func toYahooSymbol(_ id: String) -> String? {
+        guard isKorean(id) else { return nil }
+        let lower = id.lowercased()
+        let suffix = String(lower.dropFirst(prefix.count))
+        return suffix.uppercased()
+    }
+
+    /// Convert Yahoo symbol → internal ID. Always succeeds.
+    /// e.g. `005930.KS` → `kr_005930.ks`
+    static func fromYahooSymbol(_ symbol: String) -> String {
+        return prefix + symbol.lowercased()
+    }
+}
diff --git a/StockMonitorTests/Utils/KoreanStockIDTests.swift b/StockMonitorTests/Utils/KoreanStockIDTests.swift
new file mode 100644
index 0000000..ec84d47
--- /dev/null
+++ b/StockMonitorTests/Utils/KoreanStockIDTests.swift
@@ -0,0 +1,61 @@
+import XCTest
+@testable import Stockbar
+
+final class KoreanStockIDTests: XCTestCase {
+
+    // MARK: - isKoreanID
+
+    func test_isKoreanID_kospi() {
+        XCTAssertTrue(KoreanStockID.isKorean("kr_005930.ks"))
+    }
+
+    func test_isKoreanID_kosdaq() {
+        XCTAssertTrue(KoreanStockID.isKorean("kr_293490.kq"))
+    }
+
+    func test_isKoreanID_rejects_other_markets() {
+        XCTAssertFalse(KoreanStockID.isKorean("sh600000"))
+        XCTAssertFalse(KoreanStockID.isKorean("hk00700"))
+        XCTAssertFalse(KoreanStockID.isKorean("usr_aapl"))
+    }
+
+    func test_isKoreanID_rejects_empty_and_garbage() {
+        XCTAssertFalse(KoreanStockID.isKorean(""))
+        XCTAssertFalse(KoreanStockID.isKorean("kr"))
+        XCTAssertFalse(KoreanStockID.isKorean("kr_"))
+    }
+
+    // MARK: - krIDToYahooSymbol
+
+    func test_krIDToYahooSymbol_kospi() {
+        XCTAssertEqual(KoreanStockID.toYahooSymbol("kr_005930.ks"), "005930.KS")
+    }
+
+    func test_krIDToYahooSymbol_kosdaq() {
+        XCTAssertEqual(KoreanStockID.toYahooSymbol("kr_293490.kq"), "293490.KQ")
+    }
+
+    func test_krIDToYahooSymbol_handles_mixed_case_input() {
+        XCTAssertEqual(KoreanStockID.toYahooSymbol("kr_005930.KS"), "005930.KS")
+        XCTAssertEqual(KoreanStockID.toYahooSymbol("KR_005930.ks"), "005930.KS")
+    }
+
+    func test_krIDToYahooSymbol_rejects_non_korean() {
+        XCTAssertNil(KoreanStockID.toYahooSymbol("sh600000"))
+        XCTAssertNil(KoreanStockID.toYahooSymbol(""))
+    }
+
+    // MARK: - yahooSymbolToKrID
+
+    func test_yahooSymbolToKrID_kospi() {
+        XCTAssertEqual(KoreanStockID.fromYahooSymbol("005930.KS"), "kr_005930.ks")
+    }
+
+    func test_yahooSymbolToKrID_kosdaq() {
+        XCTAssertEqual(KoreanStockID.fromYahooSymbol("293490.KQ"), "kr_293490.kq")
+    }
+
+    func test_yahooSymbolToKrID_handles_lowercase_input() {
+        XCTAssertEqual(KoreanStockID.fromYahooSymbol("005930.ks"), "kr_005930.ks")
+    }
+}