added tagging system

README.md

@@ -206,6 +206,7 @@ Want to learn more?
 
 - 🎨 **[THEMES.md](documentation/THEMES.md)** - Theme customization and creating custom themes
 - ✨ **[FEATURES.md](documentation/FEATURES.md)** - Complete feature list and keyboard shortcuts
+- 🏷️ **[TAGS.md](documentation/TAGS.md)** - Organize notes with tags and combined filtering
 - 🧮 **[MATHJAX.md](documentation/MATHJAX.md)** - LaTeX/Math notation examples and syntax reference
 - 📊 **[MERMAID.md](documentation/MERMAID.md)** - Diagram creation with Mermaid (flowcharts, sequence diagrams, and more)
 - 🔌 **[PLUGINS.md](documentation/PLUGINS.md)** - Plugin system and available plugins

backend/main.py

@@ -33,6 +33,8 @@ from .utils import (
     delete_folder,
     save_uploaded_image,
     validate_path_security,
+    get_all_tags,
+    get_notes_by_tag,
 )
 from .plugins import PluginManager
 from .themes import get_available_themes, get_theme_css
@@ -325,6 +327,19 @@ async def api_documentation():
                 "body": {"oldPath": "Current folder path", "newPath": "New folder path"},
                 "response": "{ success, oldPath, newPath }"
             },
+            {
+                "method": "GET",
+                "path": "/api/tags",
+                "description": "Get all tags used across all notes with their counts",
+                "response": "{ tags: { tag_name: count, ... } }"
+            },
+            {
+                "method": "GET",
+                "path": "/api/tags/{tag_name}",
+                "description": "Get all notes that have a specific tag",
+                "parameters": {"tag_name": "Tag to filter by (case-insensitive)"},
+                "response": "{ tag, count, notes: [{ path, name, folder, tags }] }"
+            },
             {
                 "method": "GET",
                 "path": "/api/search",
@@ -626,6 +641,47 @@ async def delete_folder_endpoint(folder_path: str):
         raise HTTPException(status_code=500, detail=str(e))
 
 
+# --- Tags Endpoints ---
+
+@api_router.get("/tags")
+async def list_tags():
+    """
+    Get all tags used across all notes with their counts.
+    
+    Returns:
+        Dictionary mapping tag names to note counts
+    """
+    try:
+        tags = get_all_tags(config['storage']['notes_dir'])
+        return {"tags": tags}
+    except Exception as e:
+        raise HTTPException(status_code=500, detail=str(e))
+
+
+@api_router.get("/tags/{tag_name}")
+async def get_notes_by_tag_endpoint(tag_name: str):
+    """
+    Get all notes that have a specific tag.
+    
+    Args:
+        tag_name: The tag to filter by (case-insensitive)
+        
+    Returns:
+        List of notes matching the tag
+    """
+    try:
+        notes = get_notes_by_tag(config['storage']['notes_dir'], tag_name)
+        return {
+            "tag": tag_name,
+            "count": len(notes),
+            "notes": notes
+        }
+    except Exception as e:
+        raise HTTPException(status_code=500, detail=str(e))
+
+
+# --- Notes Endpoints ---
+
 @api_router.get("/notes")
 async def list_notes():
     """List all notes with metadata"""

backend/utils.py

@@ -6,10 +6,15 @@ import os
 import re
 import shutil
 from pathlib import Path
-from typing import List, Dict, Optional
+from typing import List, Dict, Optional, Tuple
 from datetime import datetime
 
 
+# In-memory cache for parsed tags
+# Format: {file_path: (mtime, tags)}
+_tag_cache: Dict[str, Tuple[float, List[str]]] = {}
+
+
 def validate_path_security(notes_dir: str, path: Path) -> bool:
     """
     Validate that a path is within the notes directory (security check).
@@ -81,6 +86,11 @@ def move_note(notes_dir: str, old_path: str, new_path: str) -> bool:
     if not old_full_path.exists():
         return False
     
+    # Invalidate cache for old path
+    old_key = str(old_full_path)
+    if old_key in _tag_cache:
+        del _tag_cache[old_key]
+    
     # Create parent directory if needed
     new_full_path.parent.mkdir(parents=True, exist_ok=True)
     
@@ -111,6 +121,13 @@ def move_folder(notes_dir: str, old_path: str, new_path: str) -> bool:
     if new_full_path.exists():
         return False
     
+    # Invalidate cache for all notes in this folder
+    global _tag_cache
+    old_path_str = str(old_full_path)
+    keys_to_delete = [key for key in _tag_cache.keys() if key.startswith(old_path_str)]
+    for key in keys_to_delete:
+        del _tag_cache[key]
+    
     # Create parent directory if needed
     new_full_path.parent.mkdir(parents=True, exist_ok=True)
     
@@ -145,6 +162,13 @@ def delete_folder(notes_dir: str, folder_path: str) -> bool:
             print(f"Path is not a directory: {full_path}")
             return False
         
+        # Invalidate cache for all notes in this folder
+        global _tag_cache
+        folder_path_str = str(full_path)
+        keys_to_delete = [key for key in _tag_cache.keys() if key.startswith(folder_path_str)]
+        for key in keys_to_delete:
+            del _tag_cache[key]
+        
         # Delete the folder and all its contents
         shutil.rmtree(full_path)
         print(f"Successfully deleted folder: {full_path}")
@@ -166,13 +190,17 @@ def get_all_notes(notes_dir: str) -> List[Dict]:
         relative_path = md_file.relative_to(notes_path)
         stat = md_file.stat()
         
+        # Get tags for this note (cached)
+        tags = get_tags_cached(md_file)
+        
         items.append({
             "name": md_file.stem,
             "path": str(relative_path.as_posix()),
             "folder": str(relative_path.parent.as_posix()) if str(relative_path.parent) != "." else "",
             "modified": datetime.fromtimestamp(stat.st_mtime).isoformat(),
             "size": stat.st_size,
-            "type": "note"
+            "type": "note",
+            "tags": tags
         })
     
     # Get all images
@@ -229,6 +257,11 @@ def delete_note(notes_dir: str, note_path: str) -> bool:
     if not validate_path_security(notes_dir, full_path):
         return False
     
+    # Invalidate cache for this note
+    file_key = str(full_path)
+    if file_key in _tag_cache:
+        del _tag_cache[file_key]
+    
     full_path.unlink()
     
     # Note: We don't automatically delete empty folders to preserve user's folder structure
@@ -237,7 +270,10 @@ def delete_note(notes_dir: str, note_path: str) -> bool:
 
 
 def search_notes(notes_dir: str, query: str) -> List[Dict]:
-    """Simple full-text search through all notes"""
+    """
+    Full-text search through note contents only.
+    Does NOT search in file names, folder names, or paths - only note content.
+    """
     results = []
     query_lower = query.lower()
     notes_path = Path(notes_dir)
@@ -246,7 +282,8 @@ def search_notes(notes_dir: str, query: str) -> List[Dict]:
         try:
             with open(md_file, 'r', encoding='utf-8') as f:
                 content = f.read()
-                
+            
+            # Only search in note content (not file name, folder name, or path)
             if query_lower in content.lower():
                 # Find context around match
                 lines = content.split('\n')
@@ -267,6 +304,7 @@ def search_notes(notes_dir: str, query: str) -> List[Dict]:
                 results.append({
                     "name": md_file.stem,
                     "path": str(relative_path.as_posix()),
+                    "folder": str(relative_path.parent.as_posix()) if str(relative_path.parent) != "." else "",
                     "matches": matched_lines[:3]  # Limit to 3 matches per file
                 })
         except Exception:
@@ -419,3 +457,193 @@ def get_all_images(notes_dir: str) -> List[Dict]:
     
     return images
 
+
+def parse_tags(content: str) -> List[str]:
+    """
+    Extract tags from YAML frontmatter in markdown content.
+    
+    Supported formats:
+    ---
+    tags: [python, tutorial, backend]
+    ---
+    
+    or
+    
+    ---
+    tags:
+      - python
+      - tutorial
+      - backend
+    ---
+    
+    Args:
+        content: Markdown content with optional YAML frontmatter
+        
+    Returns:
+        List of tag strings (lowercase, no duplicates)
+    """
+    tags = []
+    
+    # Check if content starts with frontmatter
+    if not content.strip().startswith('---'):
+        return tags
+    
+    try:
+        # Extract frontmatter (between first two --- markers)
+        lines = content.split('\n')
+        if lines[0].strip() != '---':
+            return tags
+        
+        # Find closing ---
+        end_idx = None
+        for i in range(1, len(lines)):
+            if lines[i].strip() == '---':
+                end_idx = i
+                break
+        
+        if end_idx is None:
+            return tags
+        
+        frontmatter_lines = lines[1:end_idx]
+        
+        # Parse tags field
+        in_tags_list = False
+        for line in frontmatter_lines:
+            stripped = line.strip()
+            
+            # Check for inline array format: tags: [tag1, tag2, tag3]
+            if stripped.startswith('tags:'):
+                rest = stripped[5:].strip()
+                if rest.startswith('[') and rest.endswith(']'):
+                    # Parse inline array
+                    tags_str = rest[1:-1]  # Remove [ and ]
+                    raw_tags = [t.strip() for t in tags_str.split(',')]
+                    tags.extend([t.lower() for t in raw_tags if t])
+                    break
+                elif rest:
+                    # Single tag without brackets
+                    tags.append(rest.lower())
+                    break
+                else:
+                    # Multi-line list format
+                    in_tags_list = True
+            elif in_tags_list:
+                if stripped.startswith('-'):
+                    # List item
+                    tag = stripped[1:].strip()
+                    if tag:
+                        tags.append(tag.lower())
+                elif stripped and not stripped.startswith('#'):
+                    # End of tags list
+                    break
+        
+        # Remove duplicates and return
+        return sorted(list(set(tags)))
+        
+    except Exception as e:
+        # If parsing fails, return empty list
+        print(f"Error parsing tags: {e}")
+        return []
+
+
+def get_tags_cached(file_path: Path) -> List[str]:
+    """
+    Get tags for a file with caching based on modification time.
+    
+    Args:
+        file_path: Path to the markdown file
+        
+    Returns:
+        List of tags from the file (cached if mtime unchanged)
+    """
+    global _tag_cache
+    
+    try:
+        # Get current modification time
+        mtime = file_path.stat().st_mtime
+        file_key = str(file_path)
+        
+        # Check cache
+        if file_key in _tag_cache:
+            cached_mtime, cached_tags = _tag_cache[file_key]
+            if cached_mtime == mtime:
+                # Cache hit! Return cached tags
+                return cached_tags
+        
+        # Cache miss or stale - parse tags
+        with open(file_path, 'r', encoding='utf-8') as f:
+            content = f.read()
+            tags = parse_tags(content)
+        
+        # Update cache
+        _tag_cache[file_key] = (mtime, tags)
+        return tags
+        
+    except Exception:
+        # If anything fails, return empty list
+        return []
+
+
+def clear_tag_cache():
+    """Clear the tag cache (useful for testing or manual cache invalidation)"""
+    global _tag_cache
+    _tag_cache.clear()
+
+
+def get_all_tags(notes_dir: str) -> Dict[str, int]:
+    """
+    Get all tags used across all notes with their count (cached).
+    
+    Args:
+        notes_dir: Directory containing notes
+        
+    Returns:
+        Dictionary mapping tag names to note counts
+    """
+    tag_counts = {}
+    notes_path = Path(notes_dir)
+    
+    for md_file in notes_path.rglob("*.md"):
+        # Get tags using cache
+        tags = get_tags_cached(md_file)
+        
+        for tag in tags:
+            tag_counts[tag] = tag_counts.get(tag, 0) + 1
+    
+    return dict(sorted(tag_counts.items()))
+
+
+def get_notes_by_tag(notes_dir: str, tag: str) -> List[Dict]:
+    """
+    Get all notes that have a specific tag (cached).
+    
+    Args:
+        notes_dir: Directory containing notes
+        tag: Tag to filter by (case-insensitive)
+        
+    Returns:
+        List of note dictionaries matching the tag
+    """
+    matching_notes = []
+    tag_lower = tag.lower()
+    notes_path = Path(notes_dir)
+    
+    for md_file in notes_path.rglob("*.md"):
+        # Get tags using cache
+        tags = get_tags_cached(md_file)
+        
+        if tag_lower in tags:
+            relative_path = md_file.relative_to(notes_path)
+            stat = md_file.stat()
+            
+            matching_notes.append({
+                "name": md_file.stem,
+                "path": str(relative_path.as_posix()),
+                "folder": str(relative_path.parent.as_posix()) if str(relative_path.parent) != "." else "",
+                "modified": datetime.fromtimestamp(stat.st_mtime).isoformat(),
+                "size": stat.st_size,
+                "tags": tags
+            })
+    
+    return matching_notes
+

documentation/FEATURES.md

@@ -73,14 +73,39 @@
 - **Event hooks** - React to note saves, deletes, searches
 - **API access** - Full access to backend functionality
 
-## 🔍 Search
+## 🏷️ Tags
 
-- **Full-text search** - Find notes by content
+Organize notes with tags defined in YAML frontmatter. See **[TAGS.md](TAGS.md)** for complete guide.
+
+### Quick Start
+```markdown
+---
+tags: [python, tutorial, backend]
+---
+
+# Your Note Content
+```
+
+### Features
+- **Click to filter** - Select tags to show matching notes
+- **Multiple tags** - Combine tags (AND logic - all must match)
+- **Tag counts** - See how many notes use each tag
+- **Collapsible panel** - Saves state across sessions
+- **Auto-sync** - Updates after saving notes
+
+## 🔍 Search & Filtering
+
+### Text Search
+- **Content-only** - Searches note contents (not file/folder names)
 - **Real-time results** - As you type
 - **Highlight matches** - See context in results
 - **In-note highlighting** - Search terms highlighted in open notes
 - **Live highlighting** - Highlights update as you type or edit
-- **Fast indexing** - Instant search across notes
+
+### Combined Filtering
+- **Tags + Search** - Combine text search with tag filters
+- **Smart display** - Shows flat list when filtering, tree view when browsing
+- **Empty states** - Clear "no matches" message with quick actions
 
 ## 🧮 Math & LaTeX Support
 

documentation/TAGS.md

@@ -0,0 +1,111 @@
+# 🏷️ Tags
+
+## Overview
+
+Organize and filter your notes using tags defined in YAML frontmatter.
+
+## Basic Usage
+
+Add tags to the top of your note:
+
+```markdown
+---
+tags: [python, tutorial]
+---
+
+# Your Note Content
+
+The rest of your note goes here...
+```
+
+## Syntax Formats
+
+### Inline Array (Recommended)
+```yaml
+---
+tags: [python, tutorial, backend]
+---
+```
+
+### Multi-line List
+```yaml
+---
+tags:
+  - python
+  - tutorial
+  - backend
+---
+```
+
+### Single Tag
+```yaml
+---
+tags: python
+---
+```
+
+## Features
+
+### Filtering
+- Click any tag in the sidebar to filter notes
+- Select multiple tags to combine filters (AND logic)
+- Only notes with ALL selected tags are shown
+- Tag count badge shows number of notes per tag
+
+### Combined Search
+- Use tags alone to filter by category
+- Use text search alone to find content
+- Combine both to narrow results (e.g., search "async" in notes tagged "python")
+
+### Display Modes
+
+| Filter Type | Display |
+|------------|---------|
+| None | Full folder tree |
+| Tags only | Flat list of matching notes |
+| Text only | Search results with matches |
+| Tags + Text | Combined filtered results |
+
+## Tips
+
+- **Tag names**: Lowercase, no spaces (e.g., `python`, `work-notes`)
+- **Consistency**: Use consistent tag names across notes
+- **Hierarchy**: Use related tags (e.g., `python`, `python-async`, `python-web`)
+- **Don't overdo it**: 3-5 tags per note is usually sufficient
+
+## Frontmatter Rules
+
+- Must start with `---` on the first line
+- Must end with `---` on its own line
+- Content between markers is YAML format
+- Frontmatter is hidden from preview
+
+## Examples
+
+### Project Organization
+```markdown
+---
+tags: [project, backend, api]
+---
+
+# API Documentation
+```
+
+### Knowledge Base
+```markdown
+---
+tags: [tutorial, beginner, docker]
+---
+
+# Getting Started with Docker
+```
+
+### Work Notes
+```markdown
+---
+tags: [meeting, q4-2024, planning]
+---
+
+# Q4 Planning Meeting Notes
+```
+

frontend/app.js

@@ -62,6 +62,12 @@ function noteApp() {
         draggedFolder: null,
         dragOverFolder: null,  // Track which folder is being hovered during drag
         
+        // Tags state
+        allTags: {},
+        selectedTags: [],
+        tagsExpanded: false,
+        tagReloadTimeout: null, // For debouncing tag reloads
+        
         // Scroll sync state
         isScrolling: false,
         
@@ -256,6 +262,7 @@ function noteApp() {
             this.loadSidebarWidth();
             this.loadEditorWidth();
             this.loadViewMode();
+            this.loadTagsExpanded();
             
             // Parse URL and load specific note if provided
             this.loadNoteFromURL();
@@ -340,6 +347,11 @@ function noteApp() {
                 }
             });
             
+            // Watch tags panel expanded state and save to localStorage
+            this.$watch('tagsExpanded', () => {
+                this.saveTagsExpanded();
+            });
+            
             // Setup keyboard shortcuts (only once to prevent double triggers)
             if (!window.__noteapp_shortcuts_initialized) {
                 window.__noteapp_shortcuts_initialized = true;
@@ -536,11 +548,196 @@ function noteApp() {
                 this.notes = data.notes;
                 this.allFolders = data.folders || [];
                 this.buildFolderTree();
+                await this.loadTags(); // Load tags after notes are loaded
             } catch (error) {
                 ErrorHandler.handle('load notes', error);
             }
         },
         
+        // Load all tags
+        async loadTags() {
+            try {
+                const response = await fetch('/api/tags');
+                const data = await response.json();
+                this.allTags = data.tags || {};
+            } catch (error) {
+                ErrorHandler.handle('load tags', error, false); // Don't show alert, tags are optional
+            }
+        },
+        
+        // Debounced tag reload (prevents excessive API calls during typing)
+        loadTagsDebounced() {
+            // Clear existing timeout
+            if (this.tagReloadTimeout) {
+                clearTimeout(this.tagReloadTimeout);
+            }
+            
+            // Set new timeout - reload tags 2 seconds after last save
+            this.tagReloadTimeout = setTimeout(() => {
+                this.loadTags();
+            }, 2000);
+        },
+        
+        // Toggle tag selection for filtering
+        toggleTag(tag) {
+            const index = this.selectedTags.indexOf(tag);
+            if (index > -1) {
+                this.selectedTags.splice(index, 1);
+            } else {
+                this.selectedTags.push(tag);
+            }
+            
+            // Apply unified filtering
+            this.applyFilters();
+        },
+        
+        // Clear all tag filters
+        clearTagFilters() {
+            this.selectedTags = [];
+            
+            // Apply unified filtering
+            this.applyFilters();
+        },
+        
+        // Unified filtering logic combining tags and text search
+        async applyFilters() {
+            const hasTextSearch = this.searchQuery.trim().length > 0;
+            const hasTagFilter = this.selectedTags.length > 0;
+            
+            // Case 1: No filters at all → show full folder tree
+            if (!hasTextSearch && !hasTagFilter) {
+                this.searchResults = [];
+                this.currentSearchHighlight = '';
+                this.clearSearchHighlights();
+                this.buildFolderTree();
+                return;
+            }
+            
+            // Case 2: Only tag filter → convert to flat list of matching notes
+            if (hasTagFilter && !hasTextSearch) {
+                this.searchResults = this.notes.filter(note => 
+                    note.type === 'note' && this.noteMatchesTags(note)
+                );
+                this.currentSearchHighlight = '';
+                this.clearSearchHighlights();
+                return;
+            }
+            
+            // Case 3: Text search (with or without tag filter)
+            if (hasTextSearch) {
+                try {
+                    const response = await fetch(`/api/search?q=${encodeURIComponent(this.searchQuery)}`);
+                    const data = await response.json();
+                    
+                    // Apply tag filtering to search results if tags are selected
+                    let results = data.results;
+                    if (hasTagFilter) {
+                        results = results.filter(result => {
+                            const note = this.notes.find(n => n.path === result.path);
+                            return note ? this.noteMatchesTags(note) : false;
+                        });
+                    }
+                    
+                    this.searchResults = results;
+                    
+                    // Highlight search term in current note if open
+                    if (this.currentNote && this.noteContent) {
+                        this.currentSearchHighlight = this.searchQuery;
+                        this.$nextTick(() => {
+                            this.highlightSearchTerm(this.searchQuery, false);
+                        });
+                    }
+                } catch (error) {
+                    console.error('Search failed:', error);
+                }
+            }
+        },
+        
+        // Check if a note matches selected tags (AND logic)
+        noteMatchesTags(note) {
+            if (this.selectedTags.length === 0) {
+                return true; // No filter active
+            }
+            if (!note.tags || note.tags.length === 0) {
+                return false; // Note has no tags but filter is active
+            }
+            // Check if note has ALL selected tags (AND logic)
+            return this.selectedTags.every(tag => note.tags.includes(tag));
+        },
+        
+        // Get all tags sorted by name
+        get sortedTags() {
+            return Object.entries(this.allTags).sort((a, b) => a[0].localeCompare(b[0]));
+        },
+        
+        // Get tags for current note
+        get currentNoteTags() {
+            if (!this.currentNote) return [];
+            const note = this.notes.find(n => n.path === this.currentNote);
+            return note && note.tags ? note.tags : [];
+        },
+        
+        // Parse tags from markdown content (matches backend logic)
+        parseTagsFromContent(content) {
+            if (!content || !content.trim().startsWith('---')) {
+                return [];
+            }
+            
+            try {
+                const lines = content.split('\n');
+                if (lines[0].trim() !== '---') return [];
+                
+                // Find closing ---
+                let endIdx = -1;
+                for (let i = 1; i < lines.length; i++) {
+                    if (lines[i].trim() === '---') {
+                        endIdx = i;
+                        break;
+                    }
+                }
+                
+                if (endIdx === -1) return [];
+                
+                const frontmatterLines = lines.slice(1, endIdx);
+                const tags = [];
+                let inTagsList = false;
+                
+                for (const line of frontmatterLines) {
+                    const stripped = line.trim();
+                    
+                    // Check for inline array: tags: [tag1, tag2]
+                    if (stripped.startsWith('tags:')) {
+                        const rest = stripped.substring(5).trim();
+                        if (rest.startsWith('[') && rest.endsWith(']')) {
+                            const tagsStr = rest.substring(1, rest.length - 1);
+                            const rawTags = tagsStr.split(',').map(t => t.trim());
+                            tags.push(...rawTags.filter(t => t).map(t => t.toLowerCase()));
+                            break;
+                        } else if (rest) {
+                            tags.push(rest.toLowerCase());
+                            break;
+                        } else {
+                            inTagsList = true;
+                        }
+                    } else if (inTagsList) {
+                        if (stripped.startsWith('-')) {
+                            const tag = stripped.substring(1).trim();
+                            if (tag && !tag.startsWith('#')) {
+                                tags.push(tag.toLowerCase());
+                            }
+                        } else if (stripped && !stripped.startsWith('#')) {
+                            break;
+                        }
+                    }
+                }
+                
+                return [...new Set(tags)].sort();
+            } catch (e) {
+                console.error('Error parsing tags:', e);
+                return [];
+            }
+        },
+        
         // Build folder tree structure
         buildFolderTree() {
             const tree = {};
@@ -565,7 +762,7 @@ function noteApp() {
                 });
             });
             
-            // Add notes to their folders
+            // Add ALL notes to their folders (no filtering - tree only shown when no filters active)
             this.notes.forEach(note => {
                 if (!note.folder) {
                     // Root level note
@@ -2072,6 +2269,17 @@ function noteApp() {
                     if (note) {
                         note.modified = new Date().toISOString();
                         note.size = new Blob([this.noteContent]).size;
+                        
+                        // Parse tags from content
+                        note.tags = this.parseTagsFromContent(this.noteContent);
+                    }
+                    
+                    // Reload tags to update sidebar counts (debounced to prevent spam)
+                    this.loadTagsDebounced();
+                    
+                    // Rebuild folder tree if tag filters are active
+                    if (this.selectedTags.length > 0) {
+                        this.buildFolderTree();
                     }
                     
                     // Hide "saved" indicator
@@ -2164,30 +2372,9 @@ function noteApp() {
         },
         
         // Search notes
+        // Search notes by text (calls unified filter logic)
         async searchNotes() {
-            if (!this.searchQuery.trim()) {
+            await this.applyFilters();
-                this.searchResults = [];
-                this.currentSearchHighlight = '';
-                this.clearSearchHighlights();
-                return;
-            }
-            
-            try {
-                const response = await fetch(`/api/search?q=${encodeURIComponent(this.searchQuery)}`);
-                const data = await response.json();
-                this.searchResults = data.results;
-                
-                // If a note is currently open, highlight the search term in real-time
-                if (this.currentNote && this.noteContent) {
-                    this.currentSearchHighlight = this.searchQuery;
-                    this.$nextTick(() => {
-                        // Don't focus editor during real-time search (false)
-                        this.highlightSearchTerm(this.searchQuery, false);
-                    });
-                }
-            } catch (error) {
-                console.error('Search failed:', error);
-            }
         },
         
         // Trigger MathJax typesetting after DOM update
@@ -2305,6 +2492,26 @@ function noteApp() {
         get renderedMarkdown() {
             if (!this.noteContent) return '<p style="color: var(--text-tertiary);">Nothing to preview yet...</p>';
             
+            // Strip YAML frontmatter from content before rendering
+            let contentToRender = this.noteContent;
+            if (contentToRender.trim().startsWith('---')) {
+                const lines = contentToRender.split('\n');
+                if (lines[0].trim() === '---') {
+                    // Find closing ---
+                    let endIdx = -1;
+                    for (let i = 1; i < lines.length; i++) {
+                        if (lines[i].trim() === '---') {
+                            endIdx = i;
+                            break;
+                        }
+                    }
+                    if (endIdx !== -1) {
+                        // Remove frontmatter (including the closing ---) and any empty lines after it
+                        contentToRender = lines.slice(endIdx + 1).join('\n').trim();
+                    }
+                }
+            }
+            
             // Configure marked with syntax highlighting
             marked.setOptions({
                 breaks: true,
@@ -2322,7 +2529,7 @@ function noteApp() {
             });
             
             // Parse markdown
-            let html = marked.parse(this.noteContent);
+            let html = marked.parse(contentToRender);
             
             // Post-process: Add target="_blank" to external links and title attributes to images
             // Parse as DOM to safely manipulate
@@ -2721,6 +2928,25 @@ function noteApp() {
             }
         },
         
+        loadTagsExpanded() {
+            try {
+                const saved = localStorage.getItem('tagsExpanded');
+                if (saved !== null) {
+                    this.tagsExpanded = saved === 'true';
+                }
+            } catch (error) {
+                console.error('Error loading tags expanded state:', error);
+            }
+        },
+        
+        saveTagsExpanded() {
+            try {
+                localStorage.setItem('tagsExpanded', this.tagsExpanded.toString());
+            } catch (error) {
+                console.error('Error saving tags expanded state:', error);
+            }
+        },
+        
         // Start resizing sidebar
         startResize(event) {
             this.isResizing = true;

frontend/index.html

@@ -753,7 +753,6 @@
                     </select>
                 </div>
                 <p class="text-xs mb-3" style="color: var(--text-secondary);" x-text="appTagline"></p>
-                
                 <!-- Logout Button (only show if auth is enabled) -->
                 <div x-data="{ authEnabled: false }" x-init="fetch('/api/config').then(r => r.json()).then(d => authEnabled = d.security?.enabled || false)">
                     <a x-show="authEnabled" 
@@ -829,6 +828,74 @@
                 </div>
             </div>
             
+            <!-- Tags Panel -->
+            <div class="border-b" style="border-color: var(--border-primary);">
+                <!-- Tags Header -->
+                <div 
+                    @click="tagsExpanded = !tagsExpanded"
+                    class="flex items-center justify-between px-3 py-2 cursor-pointer hover:bg-opacity-10 transition-colors"
+                    style="background-color: var(--bg-secondary);"
+                >
+                    <div class="flex items-center gap-2">
+                        <svg class="w-4 h-4" style="color: var(--text-tertiary);" fill="currentColor" viewBox="0 0 20 20">
+                            <path fill-rule="evenodd" d="M17.707 9.293a1 1 0 010 1.414l-7 7a1 1 0 01-1.414 0l-7-7A.997.997 0 012 10V5a3 3 0 013-3h5c.256 0 .512.098.707.293l7 7zM5 6a1 1 0 100-2 1 1 0 000 2z" clip-rule="evenodd"/>
+                        </svg>
+                        <span class="text-sm font-medium" style="color: var(--text-primary);">Tags</span>
+                        <span class="text-xs px-1.5 py-0.5 rounded" style="background-color: var(--bg-tertiary); color: var(--text-tertiary);" x-text="Object.keys(allTags).length"></span>
+                    </div>
+                    <svg 
+                        class="w-4 h-4 transform transition-transform"
+                        :class="{'rotate-180': tagsExpanded}"
+                        style="color: var(--text-tertiary);" 
+                        fill="none" 
+                        stroke="currentColor" 
+                        viewBox="0 0 24 24"
+                    >
+                        <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M19 9l-7 7-7-7"></path>
+                    </svg>
+                </div>
+                
+                <!-- Tags List -->
+                <div x-show="tagsExpanded" class="px-3 py-2 max-h-48 overflow-y-auto custom-scrollbar">
+                    <!-- Clear Filter Button -->
+                    <div x-show="selectedTags.length > 0" class="mb-2">
+                        <button 
+                            @click="clearTagFilters()"
+                            class="w-full px-2 py-1 text-xs rounded flex items-center justify-center gap-1"
+                            style="background-color: var(--accent-primary); color: white;"
+                            title="Clear tag filters"
+                        >
+                            <svg class="w-3 h-3" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                                <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M6 18L18 6M6 6l12 12"></path>
+                            </svg>
+                            Clear Filters (<span x-text="selectedTags.length"></span>)
+                        </button>
+                    </div>
+                    
+                    <!-- Tag Chips -->
+                    <div class="flex flex-wrap gap-1.5">
+                        <template x-for="[tag, count] in sortedTags" :key="tag">
+                            <button 
+                                @click="toggleTag(tag)"
+                                class="px-2 py-1 text-xs rounded-full transition-all hover:brightness-110"
+                                :style="selectedTags.includes(tag) 
+                                    ? 'background-color: var(--accent-primary); color: white; font-weight: 600;'
+                                    : 'background-color: var(--bg-tertiary); color: var(--text-primary);'"
+                                :title="`Filter by ${tag} (${count} notes)`"
+                            >
+                                <span x-text="tag"></span>
+                                <span class="opacity-75" x-text="` (${count})`"></span>
+                            </button>
+                        </template>
+                    </div>
+                    
+                    <!-- Empty State -->
+                    <div x-show="Object.keys(allTags).length === 0" class="text-xs text-center py-2" style="color: var(--text-tertiary);">
+                        No tags found. Add tags to notes using YAML frontmatter:
+                    </div>
+                </div>
+            </div>
+            
             <!-- New Item Dropdown -->
             <div class="p-3 border-b relative" style="border-color: var(--border-primary);">
                 <button 
@@ -886,7 +953,10 @@
             <div class="flex-1 overflow-y-auto custom-scrollbar">
                 <template x-if="searchResults.length > 0">
                     <div class="p-2">
-                        <div class="text-xs px-2 py-1" style="color: var(--text-tertiary);">Search Results</div>
+                        <div class="text-xs px-2 py-1 flex items-center justify-between" style="color: var(--text-tertiary);">
+                            <span x-text="searchQuery.trim() ? 'Search Results' : 'Filtered Notes'"></span>
+                            <span x-text="`${searchResults.length} note${searchResults.length === 1 ? '' : 's'}`"></span>
+                        </div>
                         <template x-for="note in searchResults" :key="note.path">
                             <div 
                                 @click="loadNote(note.path, true, searchQuery)"
@@ -902,7 +972,51 @@
                     </div>
                 </template>
                 
-                <template x-if="searchResults.length === 0">
+                <!-- No Results Message (when filters active but no matches) -->
+                <template x-if="searchResults.length === 0 && (selectedTags.length > 0 || searchQuery.trim())">
+                    <div class="p-6 text-center">
+                        <svg class="w-16 h-16 mx-auto mb-4 opacity-50" style="color: var(--text-tertiary);" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                            <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M9.172 16.172a4 4 0 015.656 0M9 10h.01M15 10h.01M21 12a9 9 0 11-18 0 9 9 0 0118 0z"></path>
+                        </svg>
+                        <h3 class="text-lg font-medium mb-2" style="color: var(--text-primary);">No matches found</h3>
+                        <p class="text-sm mb-4" style="color: var(--text-secondary);">
+                            <template x-if="searchQuery.trim() && selectedTags.length > 0">
+                                <span>No notes match both your search and selected tags</span>
+                            </template>
+                            <template x-if="searchQuery.trim() && selectedTags.length === 0">
+                                <span>No notes contain "<span x-text="searchQuery"></span>"</span>
+                            </template>
+                            <template x-if="!searchQuery.trim() && selectedTags.length > 0">
+                                <span>No notes have the selected tag<span x-text="selectedTags.length > 1 ? 's' : ''"></span></span>
+                            </template>
+                        </p>
+                        <div class="flex gap-2 justify-center">
+                            <button 
+                                x-show="searchQuery.trim()"
+                                @click="searchQuery = ''; searchNotes();"
+                                class="px-3 py-1.5 text-sm rounded transition-colors"
+                                style="background-color: var(--bg-secondary); color: var(--text-primary); border: 1px solid var(--border-primary);"
+                                onmouseover="this.style.backgroundColor='var(--bg-hover)'"
+                                onmouseout="this.style.backgroundColor='var(--bg-secondary)'"
+                            >
+                                Clear search
+                            </button>
+                            <button 
+                                x-show="selectedTags.length > 0"
+                                @click="clearTagFilters()"
+                                class="px-3 py-1.5 text-sm rounded transition-colors"
+                                style="background-color: var(--bg-secondary); color: var(--text-primary); border: 1px solid var(--border-primary);"
+                                onmouseover="this.style.backgroundColor='var(--bg-hover)'"
+                                onmouseout="this.style.backgroundColor='var(--bg-secondary)'"
+                            >
+                                Clear tags
+                            </button>
+                        </div>
+                    </div>
+                </template>
+                
+                <!-- Folder Tree (when no filters active) -->
+                <template x-if="searchResults.length === 0 && selectedTags.length === 0 && !searchQuery.trim()">
                     <div class="p-2">
                         <div class="text-xs px-2 py-1 mb-2" style="color: var(--text-tertiary);">
                             <div class="flex items-center justify-between mb-1">