diff --git a/errors.ts b/errors.ts
new file mode 100644
index 0000000..7ba85fd
--- /dev/null
+++ b/errors.ts
@@ -0,0 +1,20 @@
+export class NetworkError extends Error {
+  constructor(message: string) {
+    super(message);
+    this.name = "NetworkError";
+  }
+}
+
+export class APIError extends Error {
+  constructor(message: string, public status: number, public statusText: string) {
+    super(message);
+    this.name = "APIError";
+  }
+}
+
+export class InvalidResponseError extends Error {
+  constructor(message: string) {
+    super(message);
+    this.name = "InvalidResponseError";
+  }
+}
diff --git a/index.test.ts b/index.test.ts
index 4ba0d74..af6a782 100644
--- a/index.test.ts
+++ b/index.test.ts
@@ -1,3 +1,4 @@
+import { APIError, InvalidResponseError, NetworkError } from "./errors";
 import createRocketflagClient from "./index";
 import { FlagStatus } from "./index";
 
@@ -7,29 +8,43 @@ global.fetch = jest.fn() as jest.Mock<Promise<Response>>;
 describe("createRocketflagClient", () => {
   const apiUrl = "https://api.rocketflag.app";
   const flagId = "test-flag";
-  const userContext = { userId: "user123" };
+  const userContext = { cohort: "user123" };
 
   beforeEach(() => {
     jest.resetAllMocks();
     jest.spyOn(console, "error").mockImplementation(jest.fn());
   });
 
-  it("should create a client with default options", () => {
-    const client = createRocketflagClient();
-    expect(client).toBeDefined();
-    expect(client.getFlag).toBeDefined();
-    expect(client.getFlag).toBeInstanceOf(Function);
-  });
+  describe("custom client options", () => {
+    it("can create a client with a custom version", async () => {
+      const mockFlag: FlagStatus = { name: "Test Flag", enabled: true, id: flagId };
+      (fetch as jest.Mock).mockResolvedValue({ ok: true, json: () => Promise.resolve(mockFlag) });
+
+      const client = createRocketflagClient("v2");
+      await client.getFlag(flagId);
+
+      const expectedUrl = `${apiUrl}/v2/flags/${flagId}`;
+      const expectedURLObject = new URL(expectedUrl);
+
+      expect(fetch).toHaveBeenCalledWith(expect.objectContaining({ href: expectedURLObject.href }), { method: "GET" });
+    });
+
+    it("can create a client with a custom url", async () => {
+      const mockFlag: FlagStatus = { name: "Test Flag", enabled: true, id: flagId };
+      (fetch as jest.Mock).mockResolvedValue({ ok: true, json: () => Promise.resolve(mockFlag) });
+
+      const client = createRocketflagClient("v2", "https://example.com");
+      await client.getFlag(flagId);
+
+      const expectedUrl = `https://example.com/v2/flags/${flagId}`;
+      const expectedURLObject = new URL(expectedUrl);
 
-  it("should create a client with custom options", () => {
-    const client = createRocketflagClient("v2", "https://example.com/api");
-    expect(client).toBeDefined();
-    expect(client.getFlag).toBeDefined();
-    expect(client.getFlag).toBeInstanceOf(Function);
+      expect(fetch).toHaveBeenCalledWith(expect.objectContaining({ href: expectedURLObject.href }), { method: "GET" });
+    });
   });
 
   describe("getFlag", () => {
-    it("should fetch and cache a flag", async () => {
+    it("should fetch a flag", async () => {
       const mockFlag: FlagStatus = { name: "Test Flag", enabled: true, id: flagId };
       (fetch as jest.Mock).mockResolvedValue({ ok: true, json: () => Promise.resolve(mockFlag) });
 
@@ -37,20 +52,50 @@ describe("createRocketflagClient", () => {
       const flag = await client.getFlag(flagId, userContext);
 
       expect(fetch).toHaveBeenCalledTimes(1);
-      expect(fetch).toHaveBeenCalledWith(new URL(`${apiUrl}/v1/flags/${flagId}?userId=${userContext.userId}`), { method: "GET" });
-      expect(flag).toEqual(mockFlag);
 
-      // Fetch again to test caching
-      const cachedFlag = await client.getFlag(flagId, userContext);
-      expect(fetch).toHaveBeenCalledTimes(1); // Still only called once
-      expect(cachedFlag).toEqual(mockFlag);
+      const expectedUrl = `${apiUrl}/v1/flags/${flagId}?cohort=user123`;
+      const expectedURLObject = new URL(expectedUrl);
+
+      expect(fetch).toHaveBeenCalledWith(expect.objectContaining({ href: expectedURLObject.href }), { method: "GET" });
+      expect(flag).toEqual(mockFlag);
     });
 
-    it("should handle non-ok responses from the server", async () => {
-      (fetch as jest.Mock).mockResolvedValue({ ok: false, statusText: "Not Found" });
+    it("should fetch a flag with special characters in the query", async () => {
+      userContext.cohort = "user+testing_rocketflag@example.com";
+      const mockFlag: FlagStatus = { name: "Test Flag", enabled: true, id: flagId };
+      (fetch as jest.Mock).mockResolvedValue({ ok: true, json: () => Promise.resolve(mockFlag) });
+
+      const client = createRocketflagClient();
+      const flag = await client.getFlag(flagId, userContext);
+
+      expect(fetch).toHaveBeenCalledTimes(1);
+
+      const expectedUrl = `${apiUrl}/v1/flags/${flagId}?cohort=${"user%2Btesting_rocketflag%40example.com"}`;
+      const expectedURLObject = new URL(expectedUrl);
+
+      expect(fetch).toHaveBeenCalledWith(expect.objectContaining({ href: expectedURLObject.href }), { method: "GET" });
+      expect(flag).toEqual(mockFlag);
+    });
 
+    it("should throw an APIError on non-ok response with correct status and statusText", async () => {
+      (fetch as jest.Mock).mockResolvedValue({
+        ok: false,
+        status: 404,
+        statusText: "Flag Not Found",
+      });
       const client = createRocketflagClient();
-      await expect(client.getFlag(flagId, userContext)).rejects.toThrow("Not Found");
+      await expect(client.getFlag(flagId, userContext)).rejects.toThrow(APIError);
+      await expect(client.getFlag(flagId, userContext)).rejects.toThrow("API request failed with status 404");
+
+      try {
+        await client.getFlag(flagId, userContext);
+      } catch (error) {
+        expect(error).toBeInstanceOf(APIError);
+        if (error instanceof APIError) {
+          expect(error.status).toBe(404);
+          expect(error.statusText).toBe("Flag Not Found");
+        }
+      }
     });
 
     it("should handle invalid responses from the server", async () => {
@@ -66,5 +111,50 @@ describe("createRocketflagClient", () => {
       const client = createRocketflagClient();
       await expect(client.getFlag(flagId, userContext)).rejects.toThrow("Network error");
     });
+
+    it("should throw an error if flagId is empty", async () => {
+      const client = createRocketflagClient();
+      await expect(client.getFlag("", userContext)).rejects.toThrow("flagId is required");
+    });
+
+    it("should throw an error if flagId is not a string", async () => {
+      const client = createRocketflagClient();
+      await expect(client.getFlag(123 as any, userContext)).rejects.toThrow("flagId must be a string");
+    });
+
+    it("should throw a NetworkError on network error", async () => {
+      (fetch as jest.Mock).mockRejectedValue(new Error("Some network error"));
+      const client = createRocketflagClient();
+      await expect(client.getFlag(flagId, userContext)).rejects.toThrow(NetworkError);
+      await expect(client.getFlag(flagId, userContext)).rejects.toThrow("Some network error");
+    });
+
+    it("should throw an InvalidResponseError on invalid JSON response", async () => {
+      (fetch as jest.Mock).mockResolvedValue({ ok: true, json: () => Promise.reject(new Error("Syntax error")) });
+      const client = createRocketflagClient();
+      await expect(client.getFlag(flagId, userContext)).rejects.toThrow(InvalidResponseError);
+      await expect(client.getFlag(flagId, userContext)).rejects.toThrow("Failed to parse JSON response");
+    });
+
+    it("should throw an InvalidResponseError if response is not an object", async () => {
+      (fetch as jest.Mock).mockResolvedValue({ ok: true, json: () => Promise.resolve("not an object") });
+      const client = createRocketflagClient();
+      await expect(client.getFlag(flagId, userContext)).rejects.toThrow(InvalidResponseError);
+      await expect(client.getFlag(flagId, userContext)).rejects.toThrow("Invalid response format: response is not an object");
+    });
+
+    it("should throw an InvalidResponseError if validateFlag fails", async () => {
+      (fetch as jest.Mock).mockResolvedValue({
+        ok: true,
+        json: () =>
+          Promise.resolve({
+            name: "Test Flag",
+            enabled: true,
+            // id: flagId, // Missing ID to make it fail validation
+          }),
+      });
+      const client = createRocketflagClient();
+      await expect(client.getFlag(flagId, userContext)).rejects.toThrow(InvalidResponseError);
+    });
   });
 });
diff --git a/index.ts b/index.ts
index 0dbaa40..a3fb6e5 100644
--- a/index.ts
+++ b/index.ts
@@ -1,5 +1,10 @@
+import { APIError, InvalidResponseError, NetworkError } from "./errors";
 import { validateFlag } from "./validateFlag";
 
+const GET_METHOD = "GET";
+const DEFAULT_API_URL = "https://api.rocketflag.app";
+const DEFAULT_VERSION = "v1";
+
 export type FlagStatus = {
   name: string;
   enabled: boolean;
@@ -7,15 +12,19 @@ export type FlagStatus = {
 };
 
 interface UserContext {
-  [key: string]: string | number | boolean;
+  cohort?: string | number | boolean;
 }
 
-const createRocketflagClient = (version = "v1", apiUrl = "https://api.rocketflag.app") => {
-  const cache: { [key: string]: FlagStatus } = {};
-
+const createRocketflagClient = (version = DEFAULT_VERSION, apiUrl = DEFAULT_API_URL) => {
   const getFlag = async (flagId: string, userContext: UserContext = {}): Promise<FlagStatus> => {
-    if (cache[flagId]) {
-      return cache[flagId];
+    if (!flagId) {
+      throw new Error("flagId is required");
+    }
+    if (typeof flagId !== "string") {
+      throw new Error("flagId must be a string");
+    }
+    if (typeof userContext !== "object") {
+      throw new Error("userContext must be an object");
     }
 
     const url = new URL(`${apiUrl}/${version}/flags/${flagId}`);
@@ -23,19 +32,25 @@ const createRocketflagClient = (version = "v1", apiUrl = "https://api.rocketflag
       url.searchParams.append(key, value.toString());
     });
 
-    const raw = await fetch(url, {
-      method: "GET",
-    });
+    let raw: Response;
+    try {
+      raw = await fetch(url, { method: GET_METHOD });
+    } catch (error) {
+      throw new NetworkError(`Network error: ${error instanceof Error ? error.message : "Unknown error"}`);
+    }
 
-    if (!raw.ok) throw new Error(raw.statusText);
+    if (!raw.ok) throw new APIError(`API request failed with status ${raw.status}`, raw.status, raw.statusText);
 
-    const response: unknown = await raw.json();
+    let response: unknown;
+    try {
+      response = await raw.json();
+    } catch (error) {
+      throw new InvalidResponseError("Failed to parse JSON response");
+    }
 
-    if (!response) throw new Error("Invalid response from server");
-    if (typeof response !== "object") throw new Error("Invalid response from server");
-    if (!validateFlag(response)) throw new Error("Invalid response from server");
+    if (!response || typeof response !== "object") throw new InvalidResponseError("Invalid response format: response is not an object");
+    if (!validateFlag(response)) throw new InvalidResponseError("Invalid response from server");
 
-    cache[flagId] = response;
     return response;
   };
 
diff --git a/package.json b/package.json
index 52f4e47..f43f876 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@rocketflag/node-sdk",
-  "version": "0.1.5",
+  "version": "0.1.6",
   "author": "RocketFlag Developers (https://rocketflag.app)",
   "main": "index.js",
   "scripts": {