fix(Basic LLM Chain Node): Prevent incorrect wrapping of output (#14183)

packages/@n8n/nodes-langchain/nodes/chains/ChainLLM/ChainLlm.node.ts

@@ -34,7 +34,7 @@ export class ChainLlm implements INodeType {
 		icon: 'fa:link',
 		iconColor: 'black',
 		group: ['transform'],
-		version: [1, 1.1, 1.2, 1.3, 1.4, 1.5],
+		version: [1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6],
 		description: 'A simple chain to prompt a large language model',
 		defaults: {
 			name: 'Basic LLM Chain',
@@ -119,7 +119,7 @@ export class ChainLlm implements INodeType {
 				// Process each response and add to return data
 				responses.forEach((response) => {
 					returnData.push({
-						json: formatResponse(response),
+						json: formatResponse(response, this.getNode().typeVersion),
 					});
 				});
 			} catch (error) {

packages/@n8n/nodes-langchain/nodes/chains/ChainLLM/methods/chainExecutor.ts

@@ -1,5 +1,6 @@
 import type { BaseLanguageModel } from '@langchain/core/language_models/base';
-import { StringOutputParser } from '@langchain/core/output_parsers';
+import type { BaseLLMOutputParser } from '@langchain/core/output_parsers';
+import { JsonOutputParser, StringOutputParser } from '@langchain/core/output_parsers';
 import type { ChatPromptTemplate, PromptTemplate } from '@langchain/core/prompts';
 import type { IExecuteFunctions } from 'n8n-workflow';
 
@@ -8,6 +9,46 @@ import { getTracingConfig } from '@utils/tracing';
 import { createPromptTemplate } from './promptUtils';
 import type { ChainExecutionParams } from './types';
 
+/**
+ * Type guard to check if the LLM has a modelKwargs property(OpenAI)
+ */
+export function isModelWithResponseFormat(
+	llm: BaseLanguageModel,
+): llm is BaseLanguageModel & { modelKwargs: { response_format: { type: string } } } {
+	return (
+		'modelKwargs' in llm &&
+		!!llm.modelKwargs &&
+		typeof llm.modelKwargs === 'object' &&
+		'response_format' in llm.modelKwargs
+	);
+}
+
+/**
+ * Type guard to check if the LLM has a format property(Ollama)
+ */
+export function isModelWithFormat(
+	llm: BaseLanguageModel,
+): llm is BaseLanguageModel & { format: string } {
+	return 'format' in llm && typeof llm.format !== 'undefined';
+}
+
+/**
+ * Determines if an LLM is configured to output JSON and returns the appropriate output parser
+ */
+export function getOutputParserForLLM(
+	llm: BaseLanguageModel,
+): BaseLLMOutputParser<string | Record<string, unknown>> {
+	if (isModelWithResponseFormat(llm) && llm.modelKwargs?.response_format?.type === 'json_object') {
+		return new JsonOutputParser();
+	}
+
+	if (isModelWithFormat(llm) && llm.format === 'json') {
+		return new JsonOutputParser();
+	}
+
+	return new StringOutputParser();
+}
+
 /**
  * Creates a simple chain for LLMs without output parsers
  */
@@ -21,11 +62,10 @@ async function executeSimpleChain({
 	llm: BaseLanguageModel;
 	query: string;
 	prompt: ChatPromptTemplate | PromptTemplate;
-}): Promise<string[]> {
-	const chain = prompt
-		.pipe(llm)
-		.pipe(new StringOutputParser())
-		.withConfig(getTracingConfig(context));
+}) {
+	const outputParser = getOutputParserForLLM(llm);
+
+	const chain = prompt.pipe(llm).pipe(outputParser).withConfig(getTracingConfig(context));
 
 	// Execute the chain
 	const response = await chain.invoke({

packages/@n8n/nodes-langchain/nodes/chains/ChainLLM/methods/responseFormatter.ts

@@ -3,12 +3,10 @@ import type { IDataObject } from 'n8n-workflow';
 /**
  * Formats the response from the LLM chain into a consistent structure
  */
-export function formatResponse(response: unknown): IDataObject {
+export function formatResponse(response: unknown, version: number): IDataObject {
 	if (typeof response === 'string') {
 		return {
-			response: {
 			text: response.trim(),
-			},
 		};
 	}
 
@@ -19,9 +17,15 @@ export function formatResponse(response: unknown): IDataObject {
 	}
 
 	if (response instanceof Object) {
+		if (version >= 1.6) {
 			return response as IDataObject;
 		}
 
+		return {
+			text: JSON.stringify(response),
+		};
+	}
+
 	return {
 		response: {
 			text: response,

packages/@n8n/nodes-langchain/nodes/chains/ChainLLM/test/chainExecutor.test.ts

@@ -1,4 +1,5 @@
-import { StringOutputParser } from '@langchain/core/output_parsers';
+import type { BaseChatModel } from '@langchain/core/language_models/chat_models';
+import { JsonOutputParser, StringOutputParser } from '@langchain/core/output_parsers';
 import { ChatPromptTemplate, PromptTemplate } from '@langchain/core/prompts';
 import { FakeLLM, FakeChatModel } from '@langchain/core/utils/testing';
 import { mock } from 'jest-mock-extended';
@@ -8,6 +9,7 @@ import type { N8nOutputParser } from '@utils/output_parsers/N8nOutputParser';
 import * as tracing from '@utils/tracing';
 
 import { executeChain } from '../methods/chainExecutor';
+import * as chainExecutor from '../methods/chainExecutor';
 import * as promptUtils from '../methods/promptUtils';
 
 jest.mock('@utils/tracing', () => ({
@@ -27,6 +29,41 @@ describe('chainExecutor', () => {
 		jest.clearAllMocks();
 	});
 
+	describe('getOutputParserForLLM', () => {
+		it('should return JsonOutputParser for OpenAI-like models with json_object response format', () => {
+			const openAILikeModel = {
+				modelKwargs: {
+					response_format: {
+						type: 'json_object',
+					},
+				},
+			};
+
+			const parser = chainExecutor.getOutputParserForLLM(
+				openAILikeModel as unknown as BaseChatModel,
+			);
+			expect(parser).toBeInstanceOf(JsonOutputParser);
+		});
+
+		it('should return JsonOutputParser for Ollama models with json format', () => {
+			const ollamaLikeModel = {
+				format: 'json',
+			};
+
+			const parser = chainExecutor.getOutputParserForLLM(
+				ollamaLikeModel as unknown as BaseChatModel,
+			);
+			expect(parser).toBeInstanceOf(JsonOutputParser);
+		});
+
+		it('should return StringOutputParser for models without JSON format settings', () => {
+			const regularModel = new FakeLLM({});
+
+			const parser = chainExecutor.getOutputParserForLLM(regularModel);
+			expect(parser).toBeInstanceOf(StringOutputParser);
+		});
+	});
+
 	describe('executeChain', () => {
 		it('should execute a simple chain without output parsers', async () => {
 			const fakeLLM = new FakeLLM({ response: 'Test response' });
@@ -219,5 +256,77 @@ describe('chainExecutor', () => {
 
 			expect(result).toEqual(['Test chat response']);
 		});
+
+		it('should use JsonOutputParser for OpenAI models with json_object response format', async () => {
+			const fakeOpenAIModel = new FakeChatModel({});
+			(
+				fakeOpenAIModel as unknown as { modelKwargs: { response_format: { type: string } } }
+			).modelKwargs = {
+				response_format: { type: 'json_object' },
+			};
+
+			const mockPromptTemplate = new PromptTemplate({
+				template: '{query}',
+				inputVariables: ['query'],
+			});
+
+			const mockChain = {
+				invoke: jest.fn().mockResolvedValue('{"result": "json data"}'),
+			};
+
+			const withConfigMock = jest.fn().mockReturnValue(mockChain);
+			const pipeOutputParserMock = jest.fn().mockReturnValue({
+				withConfig: withConfigMock,
+			});
+
+			mockPromptTemplate.pipe = jest.fn().mockReturnValue({
+				pipe: pipeOutputParserMock,
+			});
+
+			(promptUtils.createPromptTemplate as jest.Mock).mockResolvedValue(mockPromptTemplate);
+
+			await executeChain({
+				context: mockContext,
+				itemIndex: 0,
+				query: 'Hello',
+				llm: fakeOpenAIModel,
+			});
+
+			expect(pipeOutputParserMock).toHaveBeenCalledWith(expect.any(JsonOutputParser));
+		});
+
+		it('should use JsonOutputParser for Ollama models with json format', async () => {
+			const fakeOllamaModel = new FakeChatModel({});
+			(fakeOllamaModel as unknown as { format: string }).format = 'json';
+
+			const mockPromptTemplate = new PromptTemplate({
+				template: '{query}',
+				inputVariables: ['query'],
+			});
+
+			const mockChain = {
+				invoke: jest.fn().mockResolvedValue('{"result": "json data"}'),
+			};
+
+			const withConfigMock = jest.fn().mockReturnValue(mockChain);
+			const pipeOutputParserMock = jest.fn().mockReturnValue({
+				withConfig: withConfigMock,
+			});
+
+			mockPromptTemplate.pipe = jest.fn().mockReturnValue({
+				pipe: pipeOutputParserMock,
+			});
+
+			(promptUtils.createPromptTemplate as jest.Mock).mockResolvedValue(mockPromptTemplate);
+
+			await executeChain({
+				context: mockContext,
+				itemIndex: 0,
+				query: 'Hello',
+				llm: fakeOllamaModel,
+			});
+
+			expect(pipeOutputParserMock).toHaveBeenCalledWith(expect.any(JsonOutputParser));
+		});
 	});
 });

packages/@n8n/nodes-langchain/nodes/chains/ChainLLM/test/responseFormatter.test.ts

@@ -3,38 +3,34 @@ import { formatResponse } from '../methods/responseFormatter';
 describe('responseFormatter', () => {
 	describe('formatResponse', () => {
 		it('should format string responses', () => {
-			const result = formatResponse('Test response');
+			const result = formatResponse('Test response', 1.6);
 			expect(result).toEqual({
-				response: {
 				text: 'Test response',
-				},
 			});
 		});
 
 		it('should trim string responses', () => {
-			const result = formatResponse('  Test response with whitespace   ');
+			const result = formatResponse('  Test response with whitespace   ', 1.6);
 			expect(result).toEqual({
-				response: {
 				text: 'Test response with whitespace',
-				},
 			});
 		});
 
 		it('should handle array responses', () => {
 			const testArray = [{ item: 1 }, { item: 2 }];
-			const result = formatResponse(testArray);
+			const result = formatResponse(testArray, 1.6);
 			expect(result).toEqual({ data: testArray });
 		});
 
 		it('should handle object responses', () => {
 			const testObject = { key: 'value', nested: { key: 'value' } };
-			const result = formatResponse(testObject);
+			const result = formatResponse(testObject, 1.6);
 			expect(result).toEqual(testObject);
 		});
 
 		it('should handle primitive non-string responses', () => {
 			const testNumber = 42;
-			const result = formatResponse(testNumber);
+			const result = formatResponse(testNumber, 1.6);
 			expect(result).toEqual({
 				response: {
 					text: 42,