diff --git a/test/error-handler.test.ts b/test/error-handler.test.ts
new file mode 100644
index 000000000..b909e81ab
--- /dev/null
+++ b/test/error-handler.test.ts
@@ -0,0 +1,76 @@
+import { afterEach, describe, expect, it, vi } from "vitest";
+
+describe("logError", () => {
+  afterEach(() => {
+    vi.unstubAllEnvs();
+    vi.resetModules();
+    vi.restoreAllMocks();
+  });
+
+  it("logs a readable message with full context in development mode", async () => {
+    vi.stubEnv("NODE_ENV", "development");
+    const errorSpy = vi.spyOn(console, "error").mockImplementation(() => {});
+
+    const { logError } = await import("@/lib/error-handler");
+    const error = new Error("GitHub webhook failed");
+
+    logError(error, {
+      endpoint: "/api/webhooks/github",
+      operation: "sync-payload",
+      userId: "user-123",
+      additionalContext: {
+        deliveryId: "evt_456",
+        installationId: 99,
+      },
+    });
+
+    expect(errorSpy).toHaveBeenCalledTimes(1);
+
+    const [message, logEntry] = errorSpy.mock.calls[0];
+
+    expect(message).toMatch(
+      /^\[[^\]]+\] \/api\/webhooks\/github - sync-payload:$/,
+    );
+    expect(logEntry).toMatchObject({
+      endpoint: "/api/webhooks/github",
+      operation: "sync-payload",
+      userId: "user-123",
+      error: "GitHub webhook failed",
+      deliveryId: "evt_456",
+      installationId: 99,
+    });
+    expect(logEntry.timestamp).toEqual(expect.any(String));
+    expect(Date.parse(logEntry.timestamp)).not.toBeNaN();
+    expect(logEntry.stack).toContain("GitHub webhook failed");
+  });
+
+  it("serializes a production-safe payload without stack traces", async () => {
+    vi.stubEnv("NODE_ENV", "production");
+    const errorSpy = vi.spyOn(console, "error").mockImplementation(() => {});
+
+    const { logError } = await import("@/lib/error-handler");
+
+    logError(new Error("Leaderboard sync exploded"), {
+      endpoint: "/api/leaderboard",
+      operation: "fetch-stats",
+      additionalContext: {
+        source: "github",
+      },
+    });
+
+    expect(errorSpy).toHaveBeenCalledTimes(1);
+
+    const [serializedLog] = errorSpy.mock.calls[0];
+    expect(typeof serializedLog).toBe("string");
+
+    const parsedLog = JSON.parse(serializedLog as string);
+    expect(parsedLog).toMatchObject({
+      endpoint: "/api/leaderboard",
+      operation: "fetch-stats",
+      error: "Leaderboard sync exploded",
+      source: "github",
+    });
+    expect(parsedLog.timestamp).toEqual(expect.any(String));
+    expect(parsedLog.stack).toBeUndefined();
+  });
+});