diff --git a/src/editor/completion-provider.ts b/src/editor/completion-provider.ts
new file mode 100644
index 000000000..23edf8035
--- /dev/null
+++ b/src/editor/completion-provider.ts
@@ -0,0 +1,49 @@
+import * as vscode from 'vscode';
+import { TextDocument, Position, CompletionItem, CompletionItemKind, Range } from 'vscode';
+
+export class FunctionBlockParameterCompletionProvider implements vscode.CompletionItemProvider {
+  
+  provideCompletionItems(
+    document: vscode.TextDocument,
+    position: vscode.Position,
+    token: vscode.CancellationToken,
+    context: vscode.CompletionContext
+  ): vscode.ProviderResult<vscode.CompletionItem[] | vscode.CompletionList> {
+    
+    const lineText = document.lineAt(position).text.substring(0, position.character);
+    
+    // Check if we're in a function block instantiation context
+    // Looking for pattern like: fb_instance : FUNCTION_BLOCK_NAME (
+    const functionBlockPattern = /([a-zA-Z_][a-zA-Z0-9_]*)\s*:\s*([a-zA-Z_][a-zA-Z0-9_]*)\s*\(\s*$/;
+    const match = lineText.match(functionBlockPattern);
+    
+    if (!match) {
+      return [];
+    }
+    
+    const instanceName = match[1];
+    const functionBlockName = match[2];
+    
+    // In a real implementation, we would look up the function block definition
+    // and extract parameter names. For now, we'll return a sample completion.
+    // TODO: Implement actual function block parameter lookup
+    const parameterNames = ['INPUT1', 'INPUT2', 'OUTPUT1'];
+    
+    const completionItems = parameterNames.map(paramName => {
+      const item = new CompletionItem(paramName, CompletionItemKind.Field);
+      item.detail = `Parameter of ${functionBlockName}`;
+      return item;
+    });
+    
+    return completionItems;
+  }
+}
+
+export function registerFunctionBlockParameterCompletionProvider(): vscode.Disposable {
+  return vscode.languages.registerCompletionItemProvider(
+    'st', // Assuming 'st' is the language identifier for Structured Text
+    new FunctionBlockParameterCompletionProvider(),
+    '(',
+    ','
+  );
+}
\ No newline at end of file
diff --git a/src/editor/completion-widget.ts b/src/editor/completion-widget.ts
new file mode 100644
index 000000000..b13cb1253
--- /dev/null
+++ b/src/editor/completion-widget.ts
@@ -0,0 +1,104 @@
+import { CompletionItem, CompletionItemKind } from 'vscode-languageserver-types';
+
+export interface FunctionBlockParameter {
+  name: string;
+  type: string;
+  documentation?: string;
+  defaultValue?: string;
+}
+
+export class CompletionWidget {
+  private container: HTMLElement;
+
+  constructor() {
+    this.container = document.createElement('div');
+    this.container.className = 'completion-widget';
+    this.container.style.display = 'none';
+    this.container.style.position = 'absolute';
+    this.container.style.zIndex = '1000';
+    this.container.style.backgroundColor = 'white';
+    this.container.style.border = '1px solid #ccc';
+    this.container.style.borderRadius = '4px';
+    this.container.style.boxShadow = '0 2px 8px rgba(0,0,0,0.1)';
+    this.container.style.maxHeight = '300px';
+    this.container.style.overflowY = 'auto';
+  }
+
+  show(items: CompletionItem[], position: { x: number; y: number }): void {
+    this.container.innerHTML = '';
+    
+    items.forEach(item => {
+      const element = document.createElement('div');
+      element.className = 'completion-item';
+      element.style.padding = '8px 12px';
+      element.style.cursor = 'pointer';
+      element.style.borderBottom = '1px solid #eee';
+      
+      element.addEventListener('mouseenter', () => {
+        element.style.backgroundColor = '#f0f0f0';
+      });
+      
+      element.addEventListener('mouseleave', () => {
+        element.style.backgroundColor = 'white';
+      });
+      
+      const label = document.createElement('div');
+      label.style.fontWeight = 'bold';
+      label.textContent = item.label;
+      
+      const detail = document.createElement('div');
+      detail.style.fontSize = '0.9em';
+      detail.style.color = '#666';
+      detail.textContent = item.detail || '';
+      
+      if (item.documentation) {
+        const doc = document.createElement('div');
+        doc.style.fontSize = '0.8em';
+        doc.style.color = '#888';
+        doc.style.marginTop = '4px';
+        
+        if (typeof item.documentation === 'string') {
+          doc.textContent = item.documentation;
+        } else if (typeof item.documentation === 'object' && item.documentation.value) {
+          doc.textContent = item.documentation.value;
+        }
+        
+        element.appendChild(label);
+        element.appendChild(detail);
+        element.appendChild(doc);
+      } else {
+        element.appendChild(label);
+        element.appendChild(detail);
+      }
+      
+      this.container.appendChild(element);
+    });
+    
+    this.container.style.left = `${position.x}px`;
+    this.container.style.top = `${position.y}px`;
+    this.container.style.display = 'block';
+  }
+
+  hide(): void {
+    this.container.style.display = 'none';
+  }
+
+  isVisible(): boolean {
+    return this.container.style.display === 'block';
+  }
+
+  getElement(): HTMLElement {
+    return this.container;
+  }
+
+  renderFunctionBlockParameters(parameters: FunctionBlockParameter[]): string {
+    return parameters.map(param => {
+      const defaultValue = param.defaultValue ? ` := ${param.defaultValue}` : '';
+      return `${param.name}: ${param.type}${defaultValue}`;
+    }).join('; ');
+  }
+}
+
+export function createCompletionWidget(): CompletionWidget {
+  return new CompletionWidget();
+}
\ No newline at end of file
diff --git a/src/editor/editor-keybindings.ts b/src/editor/editor-keybindings.ts
new file mode 100644
index 000000000..f8005d325
--- /dev/null
+++ b/src/editor/editor-keybindings.ts
@@ -0,0 +1,17 @@
+import { KeyCode, KeyMod } from 'monaco-editor';
+import { IEditorService } from './editor-service';
+
+export class EditorKeybindings {
+  constructor(private editorService: IEditorService) {}
+
+  public registerKeybindings(): void {
+    // Existing keybindings...
+    
+    // Add TAB key handling for function block parameter completion
+    this.editorService.addKeybinding({
+      key: KeyCode.Tab,
+      when: 'editorTextFocus && !editorReadonly && suggestWidgetVisible',
+      command: 'editor.action.triggerSuggest'
+    });
+  }
+}
\ No newline at end of file
diff --git a/src/parser/function-block-parser.ts b/src/parser/function-block-parser.ts
new file mode 100644
index 000000000..6b867b6da
--- /dev/null
+++ b/src/parser/function-block-parser.ts
@@ -0,0 +1,70 @@
+import { FunctionBlock, Parameter } from '../types/function-block';
+
+export class FunctionBlockParser {
+  parse(source: string): FunctionBlock[] {
+    const functionBlocks: FunctionBlock[] = [];
+    const lines = source.split('\n');
+    let currentBlock: FunctionBlock | null = null;
+    let inInterface = false;
+    
+    for (const line of lines) {
+      const trimmedLine = line.trim();
+      
+      // Check for function block declaration
+      const fbMatch = trimmedLine.match(/^FUNCTION_BLOCK\s+(\w+)/);
+      if (fbMatch) {
+        currentBlock = {
+          name: fbMatch[1],
+          parameters: []
+        };
+        inInterface = false;
+        continue;
+      }
+      
+      // Check for interface section
+      if (trimmedLine === 'VAR_INPUT' || trimmedLine === 'VAR_OUTPUT' || trimmedLine === 'VAR_IN_OUT') {
+        inInterface = true;
+        continue;
+      }
+      
+      // End of interface section
+      if (trimmedLine === 'END_VAR' && currentBlock) {
+        inInterface = false;
+        continue;
+      }
+      
+      // Parse parameters within interface
+      if (inInterface && currentBlock) {
+        const param = this.parseParameter(trimmedLine);
+        if (param) {
+          currentBlock.parameters.push(param);
+        }
+      }
+      
+      // End of function block
+      if (trimmedLine === 'END_FUNCTION_BLOCK' && currentBlock) {
+        functionBlocks.push(currentBlock);
+        currentBlock = null;
+      }
+    }
+    
+    return functionBlocks;
+  }
+  
+  private parseParameter(line: string): Parameter | null {
+    // Match parameter declaration: name: type := default_value;
+    const paramMatch = line.match(/^([\w_]+)\s*:\s*([\w_]+)(?:\s*:=\s*(.+))?;$/);
+    
+    if (!paramMatch) {
+      return null;
+    }
+    
+    const [, name, type, defaultValue] = paramMatch;
+    
+    return {
+      name,
+      type,
+      defaultValue: defaultValue ? defaultValue.trim() : undefined
+    };
+  }
+}
\ No newline at end of file