diff --git a/application/api/.eslintrc.json b/application/api/.eslintrc.json
index 4f0fbb07..bb85d170 100644
--- a/application/api/.eslintrc.json
+++ b/application/api/.eslintrc.json
@@ -10,6 +10,7 @@
     "db": "readonly",
     "bus": "readonly",
     "domain": "readonly",
-    "metarhia": "readonly"
+    "metarhia": "readonly",
+    "DomainError": "readonly"
   }
 }
diff --git a/application/api/console.1/content.d.ts b/application/api/console.1/content.d.ts
new file mode 100644
index 00000000..95abbf4a
--- /dev/null
+++ b/application/api/console.1/content.d.ts
@@ -0,0 +1,8 @@
+namespace api.console.content {
+  type Code = 'ENOTFOUND' | 'EPARSE';
+
+  class CustomError extends DomainError {
+    constructor(code?: Code);
+    toJSON(): object;
+  }
+}
diff --git a/application/api/console.1/content.js b/application/api/console.1/content.js
index 92b10df0..1eaec80f 100644
--- a/application/api/console.1/content.js
+++ b/application/api/console.1/content.js
@@ -1,9 +1,13 @@
 ({
   access: 'public',
+
   async method({ name }) {
+    // Try type: new api.console.content.CustomError('EPARSE');
     const filePath = `/content/${name}.md`;
     const buffer = application.resources.get(filePath);
     if (!buffer) return new Error('Content is not found');
     return { text: buffer.toString() };
   },
+
+  CustomError: class CustomError extends DomainError {},
 });
diff --git a/application/api/example.1/add.d.ts b/application/api/example.1/add.d.ts
new file mode 100644
index 00000000..2e583247
--- /dev/null
+++ b/application/api/example.1/add.d.ts
@@ -0,0 +1,8 @@
+namespace api.example.add {
+  type Code = 'EARGA' | 'EARGB';
+
+  class CustomError extends DomainError {
+    constructor(code?: Code);
+    toJSON(): object;
+  }
+}
diff --git a/application/api/example.1/add.js b/application/api/example.1/add.js
index 080f3d2e..50f8be88 100644
--- a/application/api/example.1/add.js
+++ b/application/api/example.1/add.js
@@ -5,9 +5,40 @@
   },
 
   method: async ({ a, b }) => {
+    new api.example.add.CustomError('EARGA');
+    if (typeof a !== 'number') return new DomainError('EARGA');
+    if (typeof b !== 'number') {
+      return new api.example.example.CustomError('EARGB');
+    }
+    if (Number.isNaN(a)) throw Error('Not a number: a');
+    if (Number.isNaN(b)) throw Error('Not a number: b');
     const result = a + b;
     return result;
   },
 
   returns: 'number',
+
+  errors: {
+    EARGA: 'Invalid argument: a',
+    EARGB: 'Invalid argument: b',
+  },
+
+  onError(error) {
+    if (error.code in this.errors) {
+      console.log(`Domain error detected: ${error.code}`);
+    }
+    return error;
+  },
+
+  onException(error) {
+    console.log(`Exception throws: ${error.message}`);
+    return error;
+  },
+
+  CustomError: class CustomError extends DomainError {
+    toJSON() {
+      const { name, code, message, stack } = this;
+      return { name, code, message, stack };
+    }
+  },
 });
diff --git a/types/global.d.ts b/types/global.d.ts
index c30a8220..c9569bd3 100644
--- a/types/global.d.ts
+++ b/types/global.d.ts
@@ -23,3 +23,27 @@ declare global {
     const pg: Database;
   }
 }
+
+export interface ErrorOptions {
+  code?: number | string;
+  cause?: Error;
+}
+
+export class Error extends global.Error {
+  constructor(message: string, options?: number | string | ErrorOptions);
+  message: string;
+  stack: string;
+  code?: number | string;
+  cause?: Error;
+}
+
+type Errors = Record<string, string>;
+
+export class DomainError extends Error {
+  constructor(code?: string, options?: number | string | ErrorOptions);
+  message: string;
+  stack: string;
+  code?: number | string;
+  cause?: Error;
+  toError(errors: Errors): Error;
+}