diff --git a/.github/workflows/lint.yml b/.github/workflows/lint.yml
index 7cdabd8..b7cb647 100644
--- a/.github/workflows/lint.yml
+++ b/.github/workflows/lint.yml
@@ -27,9 +27,7 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@v3
-      - uses: denoland/setup-deno@v1
-        with:
-          deno-version: vx.x.x
-
+      - name: Install tsc
+        run: npm install
       - name: Run xo
-        run: deno run --allow-read --allow-write --allow-net --allow-sys --allow-env npm:xo --reporter unix src/* test.ts
+        run: npx xo --reporter unix src/* test.ts
diff --git a/.xo-config.json b/.xo-config.json
index 224f9cd..84f1ca2 100644
--- a/.xo-config.json
+++ b/.xo-config.json
@@ -22,6 +22,7 @@
         }],
         "n/file-extension-in-import": "off",
         "promise-function-async": "off",
+        "default-case": "off",
         "prefer-promise-reject-errors": "off",
         "eslint-disable-next-line prefer-promise-reject-errors": "off",
         "unicorn/explicit-length-check": "off",
diff --git a/package.json b/package.json
index 71649ac..1d5f595 100644
--- a/package.json
+++ b/package.json
@@ -24,7 +24,7 @@
     "./ws-client.ts": "./src/ws-client.ts"
   },
   "devDependencies": {
-    "typescript": "^5.4.5",
-    "xo": "^0.58.0"
+    "typescript": "^5.5.4",
+    "xo": "^0.59.3"
   }
 }
diff --git a/src/rpcmessage.ts b/src/rpcmessage.ts
index cfc2cc2..813c599 100644
--- a/src/rpcmessage.ts
+++ b/src/rpcmessage.ts
@@ -11,6 +11,56 @@ const KeyParams = 1;
 const KeyResult = 2;
 const KeyError = 3;
 
+export const ERROR_CODE = 1;
+export const ERROR_MESSAGE = 2;
+export const ERROR_DATA = 3;
+
+enum ErrorCode {
+    InvalidRequest = 1,
+    MethodNotFound = 2,
+    InvalidParams = 3,
+    InternalError = 4,
+    ParseError = 5,
+    MethodCallTimeout = 6,
+    MethodCallCancelled = 7,
+    MethodCallException = 8,
+    Unknown = 9,
+    LoginRequired = 10,
+    UserIDRequired = 11,
+    NotImplemented = 12,
+}
+
+type ErrorMap = IMap<{
+    [ERROR_CODE]: Int<ErrorCode>;
+    [ERROR_MESSAGE]?: string;
+    [ERROR_DATA]?: RpcValue;
+}>;
+
+class RpcError extends Error {
+    constructor(private readonly err_info: ErrorMap) {
+        super(err_info.value[ERROR_MESSAGE]);
+    }
+
+    data() {
+        return this.err_info.value[ERROR_DATA];
+    }
+}
+
+export class ProtocolError extends Error {}
+
+export class InvalidRequest extends RpcError {}
+export class MethodNotFound extends RpcError {}
+export class InvalidParams extends RpcError {}
+export class InternalError extends RpcError {}
+export class ParseError extends RpcError {}
+export class MethodCallTimeout extends RpcError {}
+export class MethodCallCancelled extends RpcError {}
+export class MethodCallException extends RpcError {}
+export class Unknown extends RpcError {}
+export class LoginRequired extends RpcError {}
+export class UserIDRequired extends RpcError {}
+export class NotImplemented extends RpcError {}
+
 class RpcMessage {
     value: IMap;
     meta: MetaMap;
@@ -87,10 +137,40 @@ class RpcMessage {
 
     resultOrError() {
         if (this.value.value[KeyError] !== undefined) {
-            return new RpcError(this.value.value[KeyError] as ErrorMap);
+            if (!(this.value.value[KeyError] instanceof IMap)) {
+                return new ProtocolError('Response had an error, but this error was not a map');
+            }
+
+            const error_map = this.value.value[KeyError];
+            if (error_map.value[ERROR_CODE] === undefined) {
+                return new ProtocolError('Response had an error, but this error did not contain at least an error code');
+            }
+
+            const ErrorType = (() => {
+                switch ((this.value.value[KeyError] as ErrorMap).value[ERROR_CODE].value) {
+                    case ErrorCode.InvalidRequest: return InvalidRequest;
+                    case ErrorCode.MethodNotFound: return MethodNotFound;
+                    case ErrorCode.InvalidParams: return InvalidParams;
+                    case ErrorCode.InternalError: return InternalError;
+                    case ErrorCode.ParseError: return ParseError;
+                    case ErrorCode.MethodCallTimeout: return MethodCallTimeout;
+                    case ErrorCode.MethodCallCancelled: return MethodCallCancelled;
+                    case ErrorCode.MethodCallException: return MethodCallException;
+                    case ErrorCode.Unknown: return Unknown;
+                    case ErrorCode.LoginRequired: return LoginRequired;
+                    case ErrorCode.UserIDRequired: return UserIDRequired;
+                    case ErrorCode.NotImplemented: return NotImplemented;
+                }
+            })();
+
+            return new ErrorType(this.value.value[KeyError] as ErrorMap);
+        }
+
+        if (this.value.value[KeyResult] !== undefined) {
+            return this.value.value[KeyResult];
         }
 
-        return this.value.value[KeyResult];
+        return new ProtocolError('Response included neither result nor error');
     }
 
     setResult(result: RpcValue) {
@@ -110,46 +190,6 @@ class RpcMessage {
     }
 }
 
-export const ERROR_CODE = 1;
-export const ERROR_MESSAGE = 2;
-export const ERROR_DATA = 3;
-
-enum ErrorCode {
-    InvalidRequest = 1,
-    MethodNotFound = 2,
-    InvalidParams = 3,
-    InternalError = 4,
-    ParseError = 5,
-    MethodCallTimeout = 6,
-    MethodCallCancelled = 7,
-    MethodCallException = 8,
-    Unknown = 9,
-    LoginRequired = 10,
-    UserIDRequired = 11,
-    NotImplemented = 12,
-}
-
-type ErrorMap = IMap<{
-    [ERROR_CODE]: Int<ErrorCode>;
-    [ERROR_MESSAGE]?: string;
-    [ERROR_DATA]?: RpcValue;
-}>;
-
-class RpcError {
-    constructor(private readonly err_info: ErrorMap) {}
-    code() {
-        return this.err_info.value[ERROR_CODE];
-    }
-
-    message() {
-        return this.err_info.value[ERROR_MESSAGE];
-    }
-
-    data() {
-        return this.err_info.value[ERROR_DATA];
-    }
-}
-
-export type RpcResponse<T = RpcValue> = T | RpcError;
+export type RpcResponse<T = RpcValue> = T | Error;
 
 export {RpcMessage, RpcError, ErrorCode};
diff --git a/src/ws-client.ts b/src/ws-client.ts
index fb95191..4c9f685 100644
--- a/src/ws-client.ts
+++ b/src/ws-client.ts
@@ -1,6 +1,6 @@
 import {ChainPackReader, ChainpackProtocolType, ChainPackWriter} from './chainpack.ts';
 import {type CponReader, CponProtocolType, toCpon} from './cpon.ts';
-import {ERROR_MESSAGE, ErrorCode, ERROR_CODE, RpcError, RpcMessage, type RpcResponse} from './rpcmessage.ts';
+import {ERROR_MESSAGE, ErrorCode, ERROR_CODE, RpcError, RpcMessage, type RpcResponse, MethodCallTimeout} from './rpcmessage.ts';
 import {type RpcValue, type Null, Int, IMap, ShvMap} from './rpcvalue.ts';
 
 const DEFAULT_TIMEOUT = 5000;
@@ -194,7 +194,7 @@ class WsClient {
 
         const promise = new Promise<RpcResponse>(resolve => {
             this.rpcHandlers[rq_id] = {resolve, timeout_handle: self.setTimeout(() => {
-                resolve(new RpcError(new IMap({
+                resolve(new MethodCallTimeout(new IMap({
                     [ERROR_CODE]: new Int(ErrorCode.MethodCallTimeout),
                     [ERROR_MESSAGE]: `Shv call timeout after: ${this.timeout} msec.`,
                 })));