diff --git a/client/package.json b/client/package.json
index e136da7..4a39c02 100644
--- a/client/package.json
+++ b/client/package.json
@@ -14,6 +14,8 @@
     "format": "prettier --write \"src/**/*.{ts,tsx}\" \".storybook/**/*.{ts,tsx}\""
   },
   "dependencies": {
+    "@monaco-editor/react": "^4.7.0",
+    "highlight.js": "^11.11.1",
     "i18next": "^26.0.4",
     "lucide-react": "^1.7.0",
     "moment": "^2.30.1",
diff --git a/client/src/lib/hljs.ts b/client/src/lib/hljs.ts
new file mode 100644
index 0000000..d8a1cde
--- /dev/null
+++ b/client/src/lib/hljs.ts
@@ -0,0 +1,12 @@
+import hljs from 'highlight.js/lib/core';
+import javascript from 'highlight.js/lib/languages/javascript';
+import json from 'highlight.js/lib/languages/json';
+
+hljs.registerLanguage('javascript', javascript);
+hljs.registerLanguage('json', json);
+
+export default hljs;
+
+export function escapeHtml(str: string): string {
+  return str.replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;');
+}
diff --git a/client/src/pages/Page.module.css b/client/src/pages/Page.module.css
index d495478..370d20e 100644
--- a/client/src/pages/Page.module.css
+++ b/client/src/pages/Page.module.css
@@ -196,6 +196,10 @@
   max-width: 540px;
 }
 
+.formCardFull {
+  max-width: none;
+}
+
 .formFields {
   display: flex;
   flex-direction: column;
diff --git a/client/src/pages/credential/CreateCredentialPage.tsx b/client/src/pages/credential/CreateCredentialPage.tsx
index 2e56606..4d6a2e6 100644
--- a/client/src/pages/credential/CreateCredentialPage.tsx
+++ b/client/src/pages/credential/CreateCredentialPage.tsx
@@ -2,7 +2,7 @@ import { useState } from 'react';
 import { useNavigate } from 'react-router-dom';
 import { useTranslation } from 'react-i18next';
 import { credentials } from '../../api';
-import { Breadcrumbs, Button, Card, Input, Textarea } from '../../ui';
+import { Breadcrumbs, Button, Card, Input, CodeEditor } from '../../ui';
 import styles from '../Page.module.css';
 
 export function CreateCredentialPage() {
@@ -58,7 +58,7 @@ export function CreateCredentialPage() {
       {error && <p className={styles.error}>{error}</p>}
 
       <form onSubmit={handleSubmit} noValidate>
-        <Card className={styles.formCard}>
+        <Card className={styles.formCardFull}>
           <div className={styles.formFields}>
             <Input
               label={t('credentials.form_name')}
@@ -72,17 +72,23 @@ export function CreateCredentialPage() {
               required
               autoFocus
             />
-            <Textarea
-              label={t('credentials.form_data')}
-              placeholder={t('credentials.form_data_placeholder')}
-              value={data}
-              onChange={(e) => {
-                setData(e.target.value);
-                setDataError('');
-              }}
-              error={dataError || undefined}
-              rows={6}
-            />
+            <div className={styles.formField}>
+              <label className={styles.fieldLabel}>
+                {t('credentials.form_data')}
+                <span className={styles.requiredMark}> *</span>
+              </label>
+              <CodeEditor
+                language="json"
+                value={data}
+                onChange={(v) => {
+                  setData(v);
+                  setDataError('');
+                }}
+                rows={6}
+                error={!!dataError}
+              />
+              {dataError && <span className={styles.fieldError}>{dataError}</span>}
+            </div>
           </div>
 
           <div className={styles.formActions}>
diff --git a/client/src/pages/credential/CredentialDetailPage.tsx b/client/src/pages/credential/CredentialDetailPage.tsx
index 5ac28e8..9881c68 100644
--- a/client/src/pages/credential/CredentialDetailPage.tsx
+++ b/client/src/pages/credential/CredentialDetailPage.tsx
@@ -1,7 +1,8 @@
 import { useEffect, useState } from 'react';
 import { useNavigate, useParams } from 'react-router-dom';
 import { useTranslation } from 'react-i18next';
-import { Download, Pencil, Trash2 } from 'lucide-react';
+import { Upload, Pencil, Trash2 } from 'lucide-react';
+import { CodeBlock } from '../../ui';
 import { stringify as yamlStringify } from 'yaml';
 import { credentials } from '../../api';
 import type { Credential } from '../../api';
@@ -55,7 +56,7 @@ export function CredentialDetailPage() {
         {credential && (
           <div className={styles.toolbarActions}>
             <Button variant="secondary" size="sm" onClick={handleExport}>
-              <Download size={14} />
+              <Upload size={14} />
               {t('credentials.action_export')}
             </Button>
             <Button
@@ -116,15 +117,16 @@ export function CredentialDetailPage() {
             <>
               <h2 className={styles.sectionHeading}>{t('credentials.section_data')}</h2>
               <Card>
-                <pre className={styles.codeBlock}>
-                  {(() => {
+                <CodeBlock
+                  language="json"
+                  code={(() => {
                     try {
                       return JSON.stringify(JSON.parse(credential.data), null, 2);
                     } catch {
                       return credential.data;
                     }
                   })()}
-                </pre>
+                />
               </Card>
             </>
           )}
diff --git a/client/src/pages/credential/CredentialsPage.tsx b/client/src/pages/credential/CredentialsPage.tsx
index 692b5fa..27bb284 100644
--- a/client/src/pages/credential/CredentialsPage.tsx
+++ b/client/src/pages/credential/CredentialsPage.tsx
@@ -1,7 +1,7 @@
 import { useEffect, useRef, useState } from 'react';
 import { useNavigate } from 'react-router-dom';
 import { useTranslation } from 'react-i18next';
-import { Settings, Pencil, Trash2, Plus, Upload } from 'lucide-react';
+import { Settings, Pencil, Trash2, Plus, Download } from 'lucide-react';
 import { parse as yamlParse } from 'yaml';
 import { credentials } from '../../api';
 import type { Credential } from '../../api';
@@ -141,7 +141,7 @@ export function CredentialsPage() {
             onChange={handleImport}
           />
           <Button variant="secondary" size="sm" onClick={() => fileInputRef.current?.click()}>
-            <Upload size={14} />
+            <Download size={14} />
             {t('credentials.action_import')}
           </Button>
         </div>
diff --git a/client/src/pages/credential/EditCredentialPage.tsx b/client/src/pages/credential/EditCredentialPage.tsx
index e9ecc03..21de3f3 100644
--- a/client/src/pages/credential/EditCredentialPage.tsx
+++ b/client/src/pages/credential/EditCredentialPage.tsx
@@ -3,7 +3,7 @@ import { useNavigate, useParams } from 'react-router-dom';
 import { useTranslation } from 'react-i18next';
 import { credentials } from '../../api';
 import type { Credential } from '../../api';
-import { Breadcrumbs, Button, Card, Input, Textarea } from '../../ui';
+import { Breadcrumbs, Button, Card, Input, CodeEditor } from '../../ui';
 import styles from '../Page.module.css';
 
 export function EditCredentialPage() {
@@ -84,7 +84,7 @@ export function EditCredentialPage() {
 
       {!loading && credential && (
         <form onSubmit={handleSubmit} noValidate>
-          <Card className={styles.formCard}>
+          <Card className={styles.formCardFull}>
             <div className={styles.formFields}>
               <Input
                 label={t('credentials.form_name')}
@@ -98,17 +98,23 @@ export function EditCredentialPage() {
                 required
                 autoFocus
               />
-              <Textarea
-                label={t('credentials.form_data')}
-                placeholder={t('credentials.form_data_placeholder')}
-                value={data}
-                onChange={(e) => {
-                  setData(e.target.value);
-                  setDataError('');
-                }}
-                error={dataError || undefined}
-                rows={6}
-              />
+              <div className={styles.formField}>
+                <label className={styles.fieldLabel}>
+                  {t('credentials.form_data')}
+                  <span className={styles.requiredMark}> *</span>
+                </label>
+                <CodeEditor
+                  language="json"
+                  value={data}
+                  onChange={(v) => {
+                    setData(v);
+                    setDataError('');
+                  }}
+                  rows={6}
+                  error={!!dataError}
+                />
+                {dataError && <span className={styles.fieldError}>{dataError}</span>}
+              </div>
             </div>
 
             <div className={styles.formActions}>
diff --git a/client/src/pages/scenario/CreateStepPage.tsx b/client/src/pages/scenario/CreateStepPage.tsx
index add271d..12971df 100644
--- a/client/src/pages/scenario/CreateStepPage.tsx
+++ b/client/src/pages/scenario/CreateStepPage.tsx
@@ -4,7 +4,7 @@ import { useTranslation } from 'react-i18next';
 import { scenarios, steps } from '../../api';
 import type { Scenario, StepType } from '../../api';
 import type { CreateStepPayload } from '../../api/client';
-import { Breadcrumbs, Button, Card, Input, Select } from '../../ui';
+import { Breadcrumbs, Button, Card, Input, Select, CodeEditor } from '../../ui';
 import styles from '../Page.module.css';
 
 const STEP_TYPES: StepType[] = ['login', 'exec', 'sign'];
@@ -75,7 +75,7 @@ export function CreateStepPage() {
       {error && <p className={styles.error}>{error}</p>}
 
       <form onSubmit={handleSubmit} noValidate>
-        <Card className={styles.formCard}>
+        <Card className={styles.formCardFull}>
           <div className={styles.formFields}>
             <Input
               label={t('steps.form_order')}
diff --git a/client/src/pages/scenario/EditStepPage.tsx b/client/src/pages/scenario/EditStepPage.tsx
index ebe9788..03a1404 100644
--- a/client/src/pages/scenario/EditStepPage.tsx
+++ b/client/src/pages/scenario/EditStepPage.tsx
@@ -3,7 +3,7 @@ import { useNavigate, useParams } from 'react-router-dom';
 import { useTranslation } from 'react-i18next';
 import { scenarios, steps } from '../../api';
 import type { Scenario, ScenarioStep, StepType } from '../../api';
-import { Breadcrumbs, Button, Card, Input, Select } from '../../ui';
+import { Breadcrumbs, Button, Card, Input, Select, CodeEditor } from '../../ui';
 import styles from '../Page.module.css';
 
 const STEP_TYPES: StepType[] = ['login', 'exec', 'sign'];
@@ -91,7 +91,7 @@ export function EditStepPage() {
 
       {!loading && step && (
         <form onSubmit={handleSubmit} noValidate>
-          <Card className={styles.formCard}>
+          <Card className={styles.formCardFull}>
             <div className={styles.formFields}>
               <Input
                 label={t('steps.form_order')}
@@ -118,24 +118,18 @@ export function EditStepPage() {
               />
               <div className={styles.formField}>
                 <label className={styles.fieldLabel}>{t('steps.form_exec_code')}</label>
-                <textarea
-                  className={styles.textarea}
-                  rows={6}
+                <CodeEditor
                   value={execCode}
-                  onChange={(e) => setExecCode(e.target.value)}
-                  placeholder={t('steps.form_exec_code_placeholder')}
-                  spellCheck={false}
+                  onChange={setExecCode}
+                  rows={6}
                 />
               </div>
               <div className={styles.formField}>
                 <label className={styles.fieldLabel}>{t('steps.form_validate_code')}</label>
-                <textarea
-                  className={styles.textarea}
-                  rows={6}
+                <CodeEditor
                   value={validateCode}
-                  onChange={(e) => setValidateCode(e.target.value)}
-                  placeholder={t('steps.form_validate_code_placeholder')}
-                  spellCheck={false}
+                  onChange={setValidateCode}
+                  rows={6}
                 />
               </div>
             </div>
diff --git a/client/src/pages/scenario/ScenarioDetailPage.tsx b/client/src/pages/scenario/ScenarioDetailPage.tsx
index 377cb6d..c0a1202 100644
--- a/client/src/pages/scenario/ScenarioDetailPage.tsx
+++ b/client/src/pages/scenario/ScenarioDetailPage.tsx
@@ -1,7 +1,7 @@
 import { useEffect, useState } from 'react';
 import { useNavigate, useParams } from 'react-router-dom';
 import { useTranslation } from 'react-i18next';
-import { Play, Pencil, Plus, History, Trash2, Download } from 'lucide-react';
+import { Play, Pencil, Plus, History, Trash2, Upload } from 'lucide-react';
 import { stringify as yamlStringify } from 'yaml';
 import { scenarios, steps, scenarioCredentials, credentials as credentialsApi } from '../../api';
 import type { Scenario, ScenarioStep, ScenarioCredential, Credential } from '../../api';
@@ -227,7 +227,7 @@ export function ScenarioDetailPage() {
               {t('scenarios.action_runs')}
             </Button>
             <Button variant="secondary" size="sm" onClick={handleExport}>
-              <Download size={14} />
+              <Upload size={14} />
               {t('scenarios.action_export')}
             </Button>
             <Button variant="secondary" size="sm" onClick={() => navigate(`/scenarios/${id}/edit`)}>
diff --git a/client/src/pages/scenario/ScenariosPage.tsx b/client/src/pages/scenario/ScenariosPage.tsx
index c412801..787c32d 100644
--- a/client/src/pages/scenario/ScenariosPage.tsx
+++ b/client/src/pages/scenario/ScenariosPage.tsx
@@ -1,7 +1,7 @@
 import { useCallback, useEffect, useRef, useState } from 'react';
 import { useNavigate } from 'react-router-dom';
 import { useTranslation } from 'react-i18next';
-import { Play, Plus, Trash2, Upload } from 'lucide-react';
+import { Play, Plus, Trash2, Download } from 'lucide-react';
 import { parse as yamlParse } from 'yaml';
 import { scenarios } from '../../api';
 import type { Scenario } from '../../api';
@@ -99,7 +99,7 @@ export function ScenariosPage() {
             onChange={handleImport}
           />
           <Button variant="secondary" size="sm" onClick={() => fileInputRef.current?.click()}>
-            <Upload size={14} />
+            <Download size={14} />
             {t('scenarios.action_import')}
           </Button>
           <Button size="sm" onClick={() => navigate('/scenarios/new')}>
diff --git a/client/src/pages/snippet/CreateSnippetPage.tsx b/client/src/pages/snippet/CreateSnippetPage.tsx
index 83ea728..f1cbd73 100644
--- a/client/src/pages/snippet/CreateSnippetPage.tsx
+++ b/client/src/pages/snippet/CreateSnippetPage.tsx
@@ -2,7 +2,7 @@ import { useState } from 'react';
 import { useNavigate } from 'react-router-dom';
 import { useTranslation } from 'react-i18next';
 import { snippets } from '../../api';
-import { Breadcrumbs, Button, Card, Input, Textarea } from '../../ui';
+import { Breadcrumbs, Button, Card, Input, CodeEditor } from '../../ui';
 import styles from '../Page.module.css';
 
 export function CreateSnippetPage() {
@@ -59,7 +59,7 @@ export function CreateSnippetPage() {
       {error && <p className={styles.error}>{error}</p>}
 
       <form onSubmit={handleSubmit} noValidate>
-        <Card className={styles.formCard}>
+        <Card className={styles.formCardFull}>
           <div className={styles.formFields}>
             <Input
               label={t('snippets.form_name')}
@@ -84,16 +84,14 @@ export function CreateSnippetPage() {
                 {t('snippets.form_code')}
                 <span className={styles.requiredMark}> *</span>
               </label>
-              <textarea
-                className={[styles.textarea, codeError ? styles.textareaError : ''].filter(Boolean).join(' ')}
-                rows={14}
+              <CodeEditor
                 value={code}
-                onChange={(e) => {
-                  setCode(e.target.value);
+                onChange={(v) => {
+                  setCode(v);
                   setCodeError('');
                 }}
-                placeholder={t('snippets.form_code_placeholder')}
-                spellCheck={false}
+                rows={14}
+                error={!!codeError}
               />
               {codeError && <span className={styles.fieldError}>{codeError}</span>}
             </div>
diff --git a/client/src/pages/snippet/EditSnippetPage.tsx b/client/src/pages/snippet/EditSnippetPage.tsx
index d9e9967..d00aaff 100644
--- a/client/src/pages/snippet/EditSnippetPage.tsx
+++ b/client/src/pages/snippet/EditSnippetPage.tsx
@@ -3,7 +3,7 @@ import { useNavigate, useParams } from 'react-router-dom';
 import { useTranslation } from 'react-i18next';
 import { snippets } from '../../api';
 import type { Snippet } from '../../api';
-import { Breadcrumbs, Button, Card, Input } from '../../ui';
+import { Breadcrumbs, Button, Card, Input, CodeEditor } from '../../ui';
 import styles from '../Page.module.css';
 
 export function EditSnippetPage() {
@@ -83,7 +83,7 @@ export function EditSnippetPage() {
 
       {!loading && snippet && (
         <form onSubmit={handleSubmit} noValidate>
-          <Card className={styles.formCard}>
+          <Card className={styles.formCardFull}>
             <div className={styles.formFields}>
               <Input
                 label={t('snippets.form_name')}
@@ -108,16 +108,14 @@ export function EditSnippetPage() {
                   {t('snippets.form_code')}
                   <span className={styles.requiredMark}> *</span>
                 </label>
-                <textarea
-                  className={[styles.textarea, codeError ? styles.textareaError : ''].filter(Boolean).join(' ')}
-                  rows={14}
+                <CodeEditor
                   value={code}
-                  onChange={(e) => {
-                    setCode(e.target.value);
+                  onChange={(v) => {
+                    setCode(v);
                     setCodeError('');
                   }}
-                  placeholder={t('snippets.form_code_placeholder')}
-                  spellCheck={false}
+                  rows={14}
+                  error={!!codeError}
                 />
                 {codeError && <span className={styles.fieldError}>{codeError}</span>}
               </div>
diff --git a/client/src/pages/snippet/SnippetDetailPage.tsx b/client/src/pages/snippet/SnippetDetailPage.tsx
index ada6c13..92dc8f7 100644
--- a/client/src/pages/snippet/SnippetDetailPage.tsx
+++ b/client/src/pages/snippet/SnippetDetailPage.tsx
@@ -1,7 +1,8 @@
 import { useEffect, useState } from 'react';
 import { useNavigate, useParams } from 'react-router-dom';
 import { useTranslation } from 'react-i18next';
-import { Download, Pencil, Trash2 } from 'lucide-react';
+import { Upload, Pencil, Trash2 } from 'lucide-react';
+import { CodeBlock } from '../../ui';
 import { stringify as yamlStringify } from 'yaml';
 import { snippets } from '../../api';
 import type { Snippet } from '../../api';
@@ -55,7 +56,7 @@ export function SnippetDetailPage() {
         {snippet && (
           <div className={styles.toolbarActions}>
             <Button variant="secondary" size="sm" onClick={handleExport}>
-              <Download size={14} />
+              <Upload size={14} />
               {t('snippets.action_export')}
             </Button>
             <Button
@@ -114,7 +115,7 @@ export function SnippetDetailPage() {
               <h2 className={styles.sectionHeading}>{t('snippets.section_code')}</h2>
             </div>
             <Card>
-              <pre className={styles.codeBlock}>{snippet.code}</pre>
+              <CodeBlock code={snippet.code} />
             </Card>
           </div>
         </>
diff --git a/client/src/pages/snippet/SnippetsPage.tsx b/client/src/pages/snippet/SnippetsPage.tsx
index f8ed6d4..ab59c55 100644
--- a/client/src/pages/snippet/SnippetsPage.tsx
+++ b/client/src/pages/snippet/SnippetsPage.tsx
@@ -1,7 +1,7 @@
 import { useEffect, useRef, useState } from 'react';
 import { useNavigate } from 'react-router-dom';
 import { useTranslation } from 'react-i18next';
-import { Code, Pencil, Trash2, Plus, Upload } from 'lucide-react';
+import { Code, Pencil, Trash2, Plus, Download } from 'lucide-react';
 import { parse as yamlParse } from 'yaml';
 import { snippets } from '../../api';
 import type { Snippet } from '../../api';
@@ -134,7 +134,7 @@ export function SnippetsPage() {
             onChange={handleImport}
           />
           <Button variant="secondary" size="sm" onClick={() => fileInputRef.current?.click()}>
-            <Upload size={14} />
+            <Download size={14} />
             {t('snippets.action_import')}
           </Button>
         </div>
diff --git a/client/src/ui/CodeBlock/CodeBlock.module.css b/client/src/ui/CodeBlock/CodeBlock.module.css
new file mode 100644
index 0000000..6a04ed4
--- /dev/null
+++ b/client/src/ui/CodeBlock/CodeBlock.module.css
@@ -0,0 +1,76 @@
+.pre {
+  margin: 0;
+  overflow-x: auto;
+  white-space: pre-wrap;
+  word-break: break-all;
+}
+
+.code {
+  font-family: var(--font-mono, ui-monospace, 'Cascadia Code', 'Fira Code', monospace);
+  font-size: var(--font-size-sm);
+  line-height: 1.6;
+  display: block;
+  background: transparent !important;
+  color: var(--color-text);
+}
+
+/* ── highlight.js token overrides (theme-aware) ─────────────────────── */
+
+.code :global(.hljs-comment),
+.code :global(.hljs-quote) {
+  color: var(--hl-comment, #6A8072);
+  font-style: italic;
+}
+
+.code :global(.hljs-keyword),
+.code :global(.hljs-selector-tag),
+.code :global(.hljs-built_in),
+.code :global(.hljs-name),
+.code :global(.hljs-tag) {
+  color: var(--hl-keyword, #A67DCC);
+}
+
+.code :global(.hljs-string),
+.code :global(.hljs-title),
+.code :global(.hljs-section),
+.code :global(.hljs-attribute),
+.code :global(.hljs-literal),
+.code :global(.hljs-template-tag),
+.code :global(.hljs-template-variable),
+.code :global(.hljs-type),
+.code :global(.hljs-addition) {
+  color: var(--hl-string, #9BB870);
+}
+
+.code :global(.hljs-number),
+.code :global(.hljs-regexp),
+.code :global(.hljs-link) {
+  color: var(--hl-number, #E8A85F);
+}
+
+.code :global(.hljs-function),
+.code :global(.hljs-title.hljs-function_) {
+  color: var(--hl-function, #5BB8D4);
+}
+
+.code :global(.hljs-variable),
+.code :global(.hljs-params) {
+  color: var(--hl-variable, #D4A0A0);
+}
+
+.code :global(.hljs-property) {
+  color: var(--hl-property, #79C0C8);
+}
+
+.code :global(.hljs-deletion),
+.code :global(.hljs-meta) {
+  color: var(--hl-meta, #A9A3C9);
+}
+
+.code :global(.hljs-emphasis) {
+  font-style: italic;
+}
+
+.code :global(.hljs-strong) {
+  font-weight: 700;
+}
diff --git a/client/src/ui/CodeBlock/CodeBlock.tsx b/client/src/ui/CodeBlock/CodeBlock.tsx
new file mode 100644
index 0000000..45157e0
--- /dev/null
+++ b/client/src/ui/CodeBlock/CodeBlock.tsx
@@ -0,0 +1,27 @@
+import { useMemo } from 'react';
+import hljs, { escapeHtml } from '../../lib/hljs';
+import styles from './CodeBlock.module.css';
+
+export interface CodeBlockProps {
+  code: string;
+  language?: string;
+}
+
+export function CodeBlock({ code, language = 'javascript' }: CodeBlockProps) {
+  const highlighted = useMemo(() => {
+    try {
+      return hljs.highlight(code, { language }).value;
+    } catch {
+      return code.replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;');
+    }
+  }, [code, language]);
+
+  return (
+    <pre className={styles.pre}>
+      <code
+        className={`${styles.code} hljs language-${language}`}
+        dangerouslySetInnerHTML={{ __html: highlighted }}
+      />
+    </pre>
+  );
+}
diff --git a/client/src/ui/CodeEditor/CodeEditor.module.css b/client/src/ui/CodeEditor/CodeEditor.module.css
new file mode 100644
index 0000000..364c235
--- /dev/null
+++ b/client/src/ui/CodeEditor/CodeEditor.module.css
@@ -0,0 +1,18 @@
+.wrapper {
+  width: 100%;
+  border: var(--border-width) solid var(--color-border);
+  border-radius: var(--radius-md);
+  overflow: hidden;
+  resize: vertical;
+  min-height: 80px;
+  transition: border-color var(--transition), box-shadow var(--transition);
+}
+
+.focused {
+  border-color: var(--color-primary);
+  box-shadow: 0 0 0 3px color-mix(in srgb, var(--color-primary) 20%, transparent);
+}
+
+.hasError {
+  border-color: var(--color-danger);
+}
diff --git a/client/src/ui/CodeEditor/CodeEditor.tsx b/client/src/ui/CodeEditor/CodeEditor.tsx
new file mode 100644
index 0000000..e9e7610
--- /dev/null
+++ b/client/src/ui/CodeEditor/CodeEditor.tsx
@@ -0,0 +1,83 @@
+import { useState, useEffect } from 'react';
+import Editor, { OnMount } from '@monaco-editor/react';
+import styles from './CodeEditor.module.css';
+
+export interface CodeEditorProps {
+  value: string;
+  onChange: (value: string) => void;
+  language?: string;
+  rows?: number;
+  error?: boolean;
+}
+
+function useMonacoTheme() {
+  const [theme, setTheme] = useState(() =>
+    document.documentElement.getAttribute('data-theme') === 'dark' ? 'vs-dark' : 'vs-light'
+  );
+
+  useEffect(() => {
+    const observer = new MutationObserver(() => {
+      setTheme(
+        document.documentElement.getAttribute('data-theme') === 'dark' ? 'vs-dark' : 'vs-light'
+      );
+    });
+    observer.observe(document.documentElement, {
+      attributes: true,
+      attributeFilter: ['data-theme'],
+    });
+    return () => observer.disconnect();
+  }, []);
+
+  return theme;
+}
+
+export function CodeEditor({
+  value,
+  onChange,
+  language = 'javascript',
+  rows = 6,
+  error = false,
+}: CodeEditorProps) {
+  const theme = useMonacoTheme();
+  const [focused, setFocused] = useState(false);
+  const height = rows * 20 + 16;
+
+  const handleMount: OnMount = (editor) => {
+    editor.onDidFocusEditorWidget(() => setFocused(true));
+    editor.onDidBlurEditorWidget(() => setFocused(false));
+  };
+
+  return (
+    <div
+      className={[
+        styles.wrapper,
+        focused ? styles.focused : '',
+        error ? styles.hasError : '',
+      ]
+        .filter(Boolean)
+        .join(' ')}
+      style={{ height }}
+    >
+      <Editor
+        height="100%"
+        theme={theme}
+        language={language}
+        value={value}
+        onChange={(v) => onChange(v ?? '')}
+        onMount={handleMount}
+        options={{
+          minimap: { enabled: false },
+          scrollBeyondLastLine: false,
+          fontSize: 14,
+          lineHeight: 20,
+          wordWrap: 'on',
+          padding: { top: 8, bottom: 8 },
+          folding: false,
+          renderLineHighlight: 'line',
+          scrollbar: { vertical: 'auto', horizontal: 'hidden' },
+          automaticLayout: true,
+        }}
+      />
+    </div>
+  );
+}
diff --git a/client/src/ui/index.ts b/client/src/ui/index.ts
index b700fa6..1d54436 100644
--- a/client/src/ui/index.ts
+++ b/client/src/ui/index.ts
@@ -36,6 +36,12 @@ export type { PaginationProps } from './Pagination/Pagination';
 export { Search } from './Search/Search';
 export type { SearchProps } from './Search/Search';
 
+export { CodeBlock } from './CodeBlock/CodeBlock';
+export type { CodeBlockProps } from './CodeBlock/CodeBlock';
+
+export { CodeEditor } from './CodeEditor/CodeEditor';
+export type { CodeEditorProps } from './CodeEditor/CodeEditor';
+
 export { ContextMenu } from './ContextMenu/ContextMenu';
 export type { ContextMenuProps, ContextMenuItem } from './ContextMenu/ContextMenu';
 
diff --git a/package-lock.json b/package-lock.json
index 885da3d..1909c5d 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -15,6 +15,8 @@
     "client": {
       "name": "liqa-client",
       "dependencies": {
+        "@monaco-editor/react": "^4.7.0",
+        "highlight.js": "^11.11.1",
         "i18next": "^26.0.4",
         "lucide-react": "^1.7.0",
         "moment": "^2.30.1",
@@ -3063,6 +3065,29 @@
         }
       }
     },
+    "node_modules/@monaco-editor/loader": {
+      "version": "1.7.0",
+      "resolved": "https://registry.npmjs.org/@monaco-editor/loader/-/loader-1.7.0.tgz",
+      "integrity": "sha512-gIwR1HrJrrx+vfyOhYmCZ0/JcWqG5kbfG7+d3f/C1LXk2EvzAbHSg3MQ5lO2sMlo9izoAZ04shohfKLVT6crVA==",
+      "license": "MIT",
+      "dependencies": {
+        "state-local": "^1.0.6"
+      }
+    },
+    "node_modules/@monaco-editor/react": {
+      "version": "4.7.0",
+      "resolved": "https://registry.npmjs.org/@monaco-editor/react/-/react-4.7.0.tgz",
+      "integrity": "sha512-cyzXQCtO47ydzxpQtCGSQGOC8Gk3ZUeBXFAxD+CWXYFo5OqZyZUonFl0DwUlTyAfRHntBfw2p3w4s9R6oe1eCA==",
+      "license": "MIT",
+      "dependencies": {
+        "@monaco-editor/loader": "^1.5.0"
+      },
+      "peerDependencies": {
+        "monaco-editor": ">= 0.25.0 < 1",
+        "react": "^16.8.0 || ^17.0.0 || ^18.0.0 || ^19.0.0",
+        "react-dom": "^16.8.0 || ^17.0.0 || ^18.0.0 || ^19.0.0"
+      }
+    },
     "node_modules/@mozilla/readability": {
       "version": "0.6.0",
       "resolved": "https://registry.npmjs.org/@mozilla/readability/-/readability-0.6.0.tgz",
@@ -4642,6 +4667,14 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/@types/trusted-types": {
+      "version": "2.0.7",
+      "resolved": "https://registry.npmjs.org/@types/trusted-types/-/trusted-types-2.0.7.tgz",
+      "integrity": "sha512-ScaPdn1dQczgbl0QFTeTOmVHFULt394XJgOQNoyVhZ6r2vLnMLJfBPd53SB52T/3G36VI1/g2MZaX0cwDuXsfw==",
+      "license": "MIT",
+      "optional": true,
+      "peer": true
+    },
     "node_modules/@types/validator": {
       "version": "13.15.10",
       "resolved": "https://registry.npmjs.org/@types/validator/-/validator-13.15.10.tgz",
@@ -6947,6 +6980,16 @@
         "node": ">=6.0.0"
       }
     },
+    "node_modules/dompurify": {
+      "version": "3.2.7",
+      "resolved": "https://registry.npmjs.org/dompurify/-/dompurify-3.2.7.tgz",
+      "integrity": "sha512-WhL/YuveyGXJaerVlMYGWhvQswa7myDG17P7Vu65EWC05o8vfeNbvNf4d/BOvH99+ZW+LlQsc1GDKMa1vNK6dw==",
+      "license": "(MPL-2.0 OR Apache-2.0)",
+      "peer": true,
+      "optionalDependencies": {
+        "@types/trusted-types": "^2.0.7"
+      }
+    },
     "node_modules/dotenv": {
       "version": "17.2.3",
       "resolved": "https://registry.npmjs.org/dotenv/-/dotenv-17.2.3.tgz",
@@ -8564,6 +8607,15 @@
         "hermes-estree": "0.25.1"
       }
     },
+    "node_modules/highlight.js": {
+      "version": "11.11.1",
+      "resolved": "https://registry.npmjs.org/highlight.js/-/highlight.js-11.11.1.tgz",
+      "integrity": "sha512-Xwwo44whKBVCYoliBQwaPvtd/2tYFkRQtXDWj1nackaV2JPXx3L0+Jvd8/qCJ2p+ML0/XVkJ2q+Mr+UVdpJK5w==",
+      "license": "BSD-3-Clause",
+      "engines": {
+        "node": ">=12.0.0"
+      }
+    },
     "node_modules/hono": {
       "version": "4.12.12",
       "resolved": "https://registry.npmjs.org/hono/-/hono-4.12.12.tgz",
@@ -10350,6 +10402,19 @@
         "tmpl": "1.0.5"
       }
     },
+    "node_modules/marked": {
+      "version": "14.0.0",
+      "resolved": "https://registry.npmjs.org/marked/-/marked-14.0.0.tgz",
+      "integrity": "sha512-uIj4+faQ+MgHgwUW1l2PsPglZLOLOT1uErt06dAPtx2kjteLAkbsd/0FiYg/MGS+i7ZKLb7w2WClxHkzOOuryQ==",
+      "license": "MIT",
+      "peer": true,
+      "bin": {
+        "marked": "bin/marked.js"
+      },
+      "engines": {
+        "node": ">= 18"
+      }
+    },
     "node_modules/math-intrinsics": {
       "version": "1.1.0",
       "resolved": "https://registry.npmjs.org/math-intrinsics/-/math-intrinsics-1.1.0.tgz",
@@ -10532,6 +10597,17 @@
         "node": "*"
       }
     },
+    "node_modules/monaco-editor": {
+      "version": "0.55.1",
+      "resolved": "https://registry.npmjs.org/monaco-editor/-/monaco-editor-0.55.1.tgz",
+      "integrity": "sha512-jz4x+TJNFHwHtwuV9vA9rMujcZRb0CEilTEwG2rRSpe/A7Jdkuj8xPKttCgOh+v/lkHy7HsZ64oj+q3xoAFl9A==",
+      "license": "MIT",
+      "peer": true,
+      "dependencies": {
+        "dompurify": "3.2.7",
+        "marked": "14.0.0"
+      }
+    },
     "node_modules/mrmime": {
       "version": "2.0.1",
       "resolved": "https://registry.npmjs.org/mrmime/-/mrmime-2.0.1.tgz",
@@ -12315,6 +12391,12 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/state-local": {
+      "version": "1.0.7",
+      "resolved": "https://registry.npmjs.org/state-local/-/state-local-1.0.7.tgz",
+      "integrity": "sha512-HTEHMNieakEnoe33shBYcZ7NX83ACUjCu8c40iOGEZsngj9zRnkqS9j1pqQPXwobB0ZcVTk27REb7COQ0UR59w==",
+      "license": "MIT"
+    },
     "node_modules/statuses": {
       "version": "2.0.2",
       "resolved": "https://registry.npmjs.org/statuses/-/statuses-2.0.2.tgz",