diff --git a/src/adapters/file-manager-adapter.ts b/src/adapters/file-manager-adapter.ts
index 0c4e9fd..6135ca1 100644
--- a/src/adapters/file-manager-adapter.ts
+++ b/src/adapters/file-manager-adapter.ts
@@ -1,5 +1,5 @@
 import { FileManager, TAbstractFile, TFile } from 'obsidian';
-import { IFileManagerAdapter } from './interfaces';
+import { IFileManagerAdapter, FrontmatterValue } from './interfaces';
 
 export class FileManagerAdapter implements IFileManagerAdapter {
 	constructor(private fileManager: FileManager) {}
@@ -12,7 +12,7 @@ export class FileManagerAdapter implements IFileManagerAdapter {
 		await this.fileManager.trashFile(file);
 	}
 
-	async processFrontMatter(file: TFile, fn: (frontmatter: any) => void): Promise<void> {
+	async processFrontMatter(file: TFile, fn: (frontmatter: Record<string, FrontmatterValue>) => void): Promise<void> {
 		await this.fileManager.processFrontMatter(file, fn);
 	}
 }
\ No newline at end of file
diff --git a/src/adapters/interfaces.ts b/src/adapters/interfaces.ts
index cefd99c..abcd080 100644
--- a/src/adapters/interfaces.ts
+++ b/src/adapters/interfaces.ts
@@ -1,5 +1,10 @@
 import { TAbstractFile, TFile, TFolder, CachedMetadata, DataWriteOptions } from 'obsidian';
 
+/**
+ * Frontmatter data structure (YAML-compatible types)
+ */
+export type FrontmatterValue = string | number | boolean | null | FrontmatterValue[] | { [key: string]: FrontmatterValue };
+
 /**
  * Adapter interface for Obsidian Vault operations
  */
@@ -56,5 +61,5 @@ export interface IFileManagerAdapter {
 	// File operations
 	renameFile(file: TAbstractFile, newPath: string): Promise<void>;
 	trashFile(file: TAbstractFile): Promise<void>;
-	processFrontMatter(file: TFile, fn: (frontmatter: any) => void): Promise<void>;
+	processFrontMatter(file: TFile, fn: (frontmatter: Record<string, FrontmatterValue>) => void): Promise<void>;
 }
\ No newline at end of file
diff --git a/src/main.ts b/src/main.ts
index eaeb2bc..d8487b7 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -24,7 +24,11 @@ export default class MCPServerPlugin extends Plugin {
 		}
 
 		// Migrate legacy settings (remove enableCORS and allowedOrigins)
-		const legacySettings = this.settings as any;
+		interface LegacySettings extends MCPPluginSettings {
+			enableCORS?: boolean;
+			allowedOrigins?: string[];
+		}
+		const legacySettings = this.settings as LegacySettings;
 		if ('enableCORS' in legacySettings || 'allowedOrigins' in legacySettings) {
 			console.log('Migrating legacy CORS settings...');
 			delete legacySettings.enableCORS;
diff --git a/src/server/mcp-server.ts b/src/server/mcp-server.ts
index 6158eaa..cd71f93 100644
--- a/src/server/mcp-server.ts
+++ b/src/server/mcp-server.ts
@@ -4,6 +4,8 @@ import { Server } from 'http';
 import {
 	JSONRPCRequest,
 	JSONRPCResponse,
+	JSONRPCParams,
+	JSONValue,
 	ErrorCodes,
 	InitializeResult,
 	ListToolsResult,
@@ -36,11 +38,11 @@ export class MCPServer {
 		try {
 			switch (request.method) {
 				case 'initialize':
-					return this.createSuccessResponse(request.id, await this.handleInitialize(request.params));
+					return this.createSuccessResponse(request.id, await this.handleInitialize(request.params ?? {}));
 				case 'tools/list':
 					return this.createSuccessResponse(request.id, await this.handleListTools());
 				case 'tools/call':
-					return this.createSuccessResponse(request.id, await this.handleCallTool(request.params));
+					return this.createSuccessResponse(request.id, await this.handleCallTool(request.params ?? {}));
 				case 'ping':
 					return this.createSuccessResponse(request.id, {});
 				default:
@@ -52,7 +54,7 @@ export class MCPServer {
 		}
 	}
 
-	private async handleInitialize(_params: any): Promise<InitializeResult> {
+	private async handleInitialize(_params: JSONRPCParams): Promise<InitializeResult> {
 		return {
 			protocolVersion: "2024-11-05",
 			capabilities: {
@@ -71,20 +73,20 @@ export class MCPServer {
 		};
 	}
 
-	private async handleCallTool(params: any): Promise<CallToolResult> {
-		const { name, arguments: args } = params;
-		return await this.toolRegistry.callTool(name, args);
+	private async handleCallTool(params: JSONRPCParams): Promise<CallToolResult> {
+		const paramsObj = params as { name: string; arguments: Record<string, unknown> };
+		return await this.toolRegistry.callTool(paramsObj.name, paramsObj.arguments);
 	}
 
-	private createSuccessResponse(id: string | number | undefined, result: any): JSONRPCResponse {
+	private createSuccessResponse(id: string | number | undefined, result: unknown): JSONRPCResponse {
 		return {
 			jsonrpc: "2.0",
 			id: id ?? null,
-			result
+			result: result as JSONValue
 		};
 	}
 
-	private createErrorResponse(id: string | number | undefined | null, code: number, message: string, data?: any): JSONRPCResponse {
+	private createErrorResponse(id: string | number | undefined | null, code: number, message: string, data?: JSONValue): JSONRPCResponse {
 		return {
 			jsonrpc: "2.0",
 			id: id ?? null,
@@ -104,7 +106,7 @@ export class MCPServer {
 					resolve();
 				});
 
-				this.server.on('error', (error: any) => {
+				this.server.on('error', (error: NodeJS.ErrnoException) => {
 					if (error.code === 'EADDRINUSE') {
 						reject(new Error(`Port ${this.settings.port} is already in use`));
 					} else {
diff --git a/src/server/middleware.ts b/src/server/middleware.ts
index dda6c88..234bc65 100644
--- a/src/server/middleware.ts
+++ b/src/server/middleware.ts
@@ -1,10 +1,10 @@
-import { Express, Request, Response } from 'express';
+import { Express, Request, Response, NextFunction } from 'express';
 import express from 'express';
 import cors from 'cors';
 import { MCPServerSettings } from '../types/settings-types';
-import { ErrorCodes } from '../types/mcp-types';
+import { ErrorCodes, JSONRPCResponse } from '../types/mcp-types';
 
-export function setupMiddleware(app: Express, settings: MCPServerSettings, createErrorResponse: (id: any, code: number, message: string) => any): void {
+export function setupMiddleware(app: Express, settings: MCPServerSettings, createErrorResponse: (id: string | number | null, code: number, message: string) => JSONRPCResponse): void {
 	// Parse JSON bodies
 	app.use(express.json());
 
@@ -29,7 +29,7 @@ export function setupMiddleware(app: Express, settings: MCPServerSettings, creat
 	app.use(cors(corsOptions));
 
 	// Authentication middleware - Always enabled
-	app.use((req: Request, res: Response, next: any) => {
+	app.use((req: Request, res: Response, next: NextFunction) => {
 		// Defensive check: if no API key is set, reject all requests
 		if (!settings.apiKey || settings.apiKey.trim() === '') {
 			return res.status(500).json(createErrorResponse(null, ErrorCodes.InternalError, 'Server misconfigured: No API key set'));
@@ -45,7 +45,7 @@ export function setupMiddleware(app: Express, settings: MCPServerSettings, creat
 	});
 
 	// Origin validation for security (DNS rebinding protection)
-	app.use((req: Request, res: Response, next: any) => {
+	app.use((req: Request, res: Response, next: NextFunction) => {
 		const host = req.headers.host;
 
 		// Only allow localhost connections
diff --git a/src/server/routes.ts b/src/server/routes.ts
index b924a4c..20e3a52 100644
--- a/src/server/routes.ts
+++ b/src/server/routes.ts
@@ -2,9 +2,9 @@ import { Express, Request, Response } from 'express';
 import { JSONRPCRequest, JSONRPCResponse, ErrorCodes } from '../types/mcp-types';
 
 export function setupRoutes(
-	app: Express, 
+	app: Express,
 	handleRequest: (request: JSONRPCRequest) => Promise<JSONRPCResponse>,
-	createErrorResponse: (id: any, code: number, message: string) => JSONRPCResponse
+	createErrorResponse: (id: string | number | null, code: number, message: string) => JSONRPCResponse
 ): void {
 	// Main MCP endpoint
 	app.post('/mcp', async (req: Request, res: Response) => {
diff --git a/src/tools/index.ts b/src/tools/index.ts
index 6af000d..3445a32 100644
--- a/src/tools/index.ts
+++ b/src/tools/index.ts
@@ -474,6 +474,7 @@ export class ToolRegistry {
 		];
 	}
 
+	// eslint-disable-next-line @typescript-eslint/no-explicit-any
 	async callTool(name: string, args: any): Promise<CallToolResult> {
 		const startTime = Date.now();
 		
diff --git a/src/tools/note-tools.ts b/src/tools/note-tools.ts
index 852f19f..68a2c9e 100644
--- a/src/tools/note-tools.ts
+++ b/src/tools/note-tools.ts
@@ -13,7 +13,7 @@ import {
 } from '../types/mcp-types';
 import { PathUtils } from '../utils/path-utils';
 import { ErrorMessages } from '../utils/error-messages';
-import { FrontmatterUtils } from '../utils/frontmatter-utils';
+import { FrontmatterUtils, YAMLValue } from '../utils/frontmatter-utils';
 import { WaypointUtils } from '../utils/waypoint-utils';
 import { VersionUtils } from '../utils/version-utils';
 import { ContentUtils } from '../utils/content-utils';
@@ -364,16 +364,28 @@ export class NoteTools {
 			await this.vault.modify(file, content);
 
 			// Build response with word count and link validation
-			const result: any = {
+			interface UpdateNoteResult {
+				success: boolean;
+				path: string;
+				versionId: string;
+				modified: number;
+				wordCount?: number;
+				linkValidation?: {
+					valid: string[];
+					brokenNotes: Array<{ link: string; line: number; context: string }>;
+					brokenHeadings: Array<{ link: string; line: number; context: string; note: string }>;
+					summary: string;
+				};
+			}
+
+			const result: UpdateNoteResult = {
 				success: true,
 				path: file.path,
 				versionId: VersionUtils.generateVersionId(file),
-				modified: file.stat.mtime
+				modified: file.stat.mtime,
+				wordCount: ContentUtils.countWords(content)
 			};
 
-			// Add word count
-			result.wordCount = ContentUtils.countWords(content);
-
 			// Add link validation if requested
 			if (validateLinks) {
 				result.linkValidation = await LinkUtils.validateLinks(
@@ -731,7 +743,7 @@ export class NoteTools {
 	 */
 	async updateFrontmatter(
 		path: string,
-		patch?: Record<string, any>,
+		patch?: Record<string, YAMLValue>,
 		remove: string[] = [],
 		ifMatch?: string
 	): Promise<CallToolResult> {
diff --git a/src/tools/vault-tools.ts b/src/tools/vault-tools.ts
index ae192bc..56361e5 100644
--- a/src/tools/vault-tools.ts
+++ b/src/tools/vault-tools.ts
@@ -385,8 +385,10 @@ export class VaultTools {
 		// In most cases, this will be 0 for directories
 		let modified = 0;
 		try {
-			if ((folder as any).stat && typeof (folder as any).stat.mtime === 'number') {
-				modified = (folder as any).stat.mtime;
+			// TFolder doesn't officially have stat, but it may exist in practice
+			const folderWithStat = folder as TFolder & { stat?: { mtime?: number } };
+			if (folderWithStat.stat && typeof folderWithStat.stat.mtime === 'number') {
+				modified = folderWithStat.stat.mtime;
 			}
 		} catch (error) {
 			// Silently fail - modified will remain 0
diff --git a/src/types/mcp-types.ts b/src/types/mcp-types.ts
index ebcb0bb..7e5b62a 100644
--- a/src/types/mcp-types.ts
+++ b/src/types/mcp-types.ts
@@ -1,22 +1,39 @@
 // MCP Protocol Types
+
+/**
+ * JSON-RPC compatible value types
+ */
+export type JSONValue =
+	| string
+	| number
+	| boolean
+	| null
+	| JSONValue[]
+	| { [key: string]: JSONValue };
+
+/**
+ * JSON-RPC parameters can be an object or array
+ */
+export type JSONRPCParams = { [key: string]: JSONValue } | JSONValue[];
+
 export interface JSONRPCRequest {
 	jsonrpc: "2.0";
 	id?: string | number;
 	method: string;
-	params?: any;
+	params?: JSONRPCParams;
 }
 
 export interface JSONRPCResponse {
 	jsonrpc: "2.0";
 	id: string | number | null;
-	result?: any;
+	result?: JSONValue;
 	error?: JSONRPCError;
 }
 
 export interface JSONRPCError {
 	code: number;
 	message: string;
-	data?: any;
+	data?: JSONValue;
 }
 
 export enum ErrorCodes {
@@ -38,12 +55,25 @@ export interface InitializeResult {
 	};
 }
 
+/**
+ * JSON Schema property definition
+ */
+export interface JSONSchemaProperty {
+	type: string;
+	description?: string;
+	enum?: string[];
+	items?: JSONSchemaProperty;
+	properties?: Record<string, JSONSchemaProperty>;
+	required?: string[];
+	[key: string]: string | string[] | JSONSchemaProperty | Record<string, JSONSchemaProperty> | undefined;
+}
+
 export interface Tool {
 	name: string;
 	description: string;
 	inputSchema: {
 		type: string;
-		properties: Record<string, any>;
+		properties: Record<string, JSONSchemaProperty>;
 		required?: string[];
 	};
 }
@@ -160,7 +190,7 @@ export interface FrontmatterSummary {
 	title?: string;
 	tags?: string[];
 	aliases?: string[];
-	[key: string]: any;
+	[key: string]: JSONValue | undefined;
 }
 
 export interface FileMetadataWithFrontmatter extends FileMetadata {
@@ -179,7 +209,7 @@ export interface ParsedNote {
 	path: string;
 	hasFrontmatter: boolean;
 	frontmatter?: string;
-	parsedFrontmatter?: Record<string, any>;
+	parsedFrontmatter?: Record<string, JSONValue>;
 	content: string;
 	contentWithoutFrontmatter?: string;
 	wordCount?: number;
@@ -200,9 +230,9 @@ export interface ExcalidrawMetadata {
 	hasCompressedData?: boolean;
 	/** Drawing metadata including appState and version */
 	metadata?: {
-		appState?: Record<string, any>;
+		appState?: Record<string, JSONValue>;
 		version?: number;
-		[key: string]: any;
+		[key: string]: JSONValue | undefined;
 	};
 	/** Preview text extracted from text elements section (when includePreview=true) */
 	preview?: string;
diff --git a/src/ui/notifications.ts b/src/ui/notifications.ts
index 34a702a..0dbab1c 100644
--- a/src/ui/notifications.ts
+++ b/src/ui/notifications.ts
@@ -7,6 +7,7 @@ import { MCPPluginSettings } from '../types/settings-types';
 export interface NotificationHistoryEntry {
 	timestamp: number;
 	toolName: string;
+	// eslint-disable-next-line @typescript-eslint/no-explicit-any
 	args: any;
 	success: boolean;
 	duration?: number;
@@ -74,6 +75,7 @@ export class NotificationManager {
 	/**
 	 * Show notification for tool call start
 	 */
+	// eslint-disable-next-line @typescript-eslint/no-explicit-any
 	showToolCall(toolName: string, args: any, duration?: number): void {
 		if (!this.shouldShowNotification()) {
 			return;
@@ -140,6 +142,7 @@ export class NotificationManager {
 	/**
 	 * Format arguments for display
 	 */
+	// eslint-disable-next-line @typescript-eslint/no-explicit-any
 	private formatArgs(args: any): string {
 		if (!this.settings.showParameters) {
 			return '';
diff --git a/src/utils/encryption-utils.ts b/src/utils/encryption-utils.ts
index 39c8c4e..f729acc 100644
--- a/src/utils/encryption-utils.ts
+++ b/src/utils/encryption-utils.ts
@@ -1,5 +1,12 @@
+// Define Electron SafeStorage interface
+interface ElectronSafeStorage {
+	isEncryptionAvailable(): boolean;
+	encryptString(plainText: string): Buffer;
+	decryptString(encrypted: Buffer): string;
+}
+
 // Safely import safeStorage - may not be available in all environments
-let safeStorage: any = null;
+let safeStorage: ElectronSafeStorage | null = null;
 try {
 	const electron = require('electron');
 	safeStorage = electron.safeStorage || null;
@@ -35,7 +42,7 @@ export function encryptApiKey(apiKey: string): string {
 	}
 
 	try {
-		const encrypted = safeStorage.encryptString(apiKey);
+		const encrypted = safeStorage!.encryptString(apiKey);
 		return `encrypted:${encrypted.toString('base64')}`;
 	} catch (error) {
 		console.error('Failed to encrypt API key, falling back to plaintext:', error);
diff --git a/src/utils/frontmatter-utils.ts b/src/utils/frontmatter-utils.ts
index a1cf135..1eb6dd1 100644
--- a/src/utils/frontmatter-utils.ts
+++ b/src/utils/frontmatter-utils.ts
@@ -1,5 +1,16 @@
 import { parseYaml } from 'obsidian';
 
+/**
+ * YAML value types that can appear in frontmatter
+ */
+export type YAMLValue =
+	| string
+	| number
+	| boolean
+	| null
+	| YAMLValue[]
+	| { [key: string]: YAMLValue };
+
 /**
  * Utility class for parsing and extracting frontmatter from markdown files
  */
@@ -11,7 +22,7 @@ export class FrontmatterUtils {
 	static extractFrontmatter(content: string): {
 		hasFrontmatter: boolean;
 		frontmatter: string;
-		parsedFrontmatter: Record<string, any> | null;
+		parsedFrontmatter: Record<string, YAMLValue> | null;
 		content: string;
 		contentWithoutFrontmatter: string;
 	} {
@@ -59,7 +70,7 @@ export class FrontmatterUtils {
 		const contentWithoutFrontmatter = contentLines.join('\n');
 
 		// Parse YAML using Obsidian's built-in parser
-		let parsedFrontmatter: Record<string, any> | null = null;
+		let parsedFrontmatter: Record<string, YAMLValue> | null = null;
 		try {
 			parsedFrontmatter = parseYaml(frontmatter) || {};
 		} catch (error) {
@@ -80,17 +91,17 @@ export class FrontmatterUtils {
 	 * Extract only the frontmatter summary (common fields)
 	 * Useful for list operations without reading full content
 	 */
-	static extractFrontmatterSummary(parsedFrontmatter: Record<string, any> | null): {
+	static extractFrontmatterSummary(parsedFrontmatter: Record<string, YAMLValue> | null): {
 		title?: string;
 		tags?: string[];
 		aliases?: string[];
-		[key: string]: any;
+		[key: string]: YAMLValue | undefined;
 	} | null {
 		if (!parsedFrontmatter) {
 			return null;
 		}
 
-		const summary: Record<string, any> = {};
+		const summary: Record<string, YAMLValue> = {};
 
 		// Extract common fields
 		if (parsedFrontmatter.title) {
@@ -136,7 +147,7 @@ export class FrontmatterUtils {
 	 * Serialize frontmatter object to YAML string with delimiters
 	 * Returns the complete frontmatter block including --- delimiters
 	 */
-	static serializeFrontmatter(data: Record<string, any>): string {
+	static serializeFrontmatter(data: Record<string, YAMLValue>): string {
 		if (!data || Object.keys(data).length === 0) {
 			return '';
 		}
@@ -203,7 +214,7 @@ export class FrontmatterUtils {
 		isExcalidraw: boolean;
 		elementCount?: number;
 		hasCompressedData?: boolean;
-		metadata?: Record<string, any>;
+		metadata?: Record<string, YAMLValue>;
 	} {
 		try {
 			// Excalidraw files are typically markdown with a code block containing JSON
@@ -287,7 +298,7 @@ export class FrontmatterUtils {
 
 			// Check if data is compressed (base64 encoded)
 			const trimmedJson = jsonString.trim();
-			let jsonData: any;
+			let jsonData: Record<string, YAMLValue>;
 			
 			if (trimmedJson.startsWith('N4KAk') || !trimmedJson.startsWith('{')) {
 				// Data is compressed - try to decompress
@@ -328,9 +339,9 @@ export class FrontmatterUtils {
 			
 			// Parse the JSON (uncompressed format)
 			jsonData = JSON.parse(trimmedJson);
-			
+
 			// Count elements
-			const elementCount = jsonData.elements ? jsonData.elements.length : 0;
+			const elementCount = Array.isArray(jsonData.elements) ? jsonData.elements.length : 0;
 			
 			// Check for compressed data (files or images)
 			const hasCompressedData = !!(jsonData.files && Object.keys(jsonData.files).length > 0);