fix(Structured Output Parser Node, Auto-fixing Output Parser Node, Tools Agent Node): Structured output improvements (#13908)

Co-authored-by: Oleg Ivaniv <me@olegivaniv.com>

packages/@n8n/nodes-langchain/utils/helpers.ts

@@ -221,3 +221,22 @@ export const getConnectedTools = async (
 
 	return finalTools;
 };
+
+/**
+ * Sometimes model output is wrapped in an additional object property.
+ * This function unwraps the output if it is in the format { output: { output: { ... } } }
+ */
+export function unwrapNestedOutput(output: Record<string, unknown>): Record<string, unknown> {
+	if (
+		'output' in output &&
+		Object.keys(output).length === 1 &&
+		typeof output.output === 'object' &&
+		output.output !== null &&
+		'output' in output.output &&
+		Object.keys(output.output).length === 1
+	) {
+		return output.output as Record<string, unknown>;
+	}
+
+	return output;
+}

packages/@n8n/nodes-langchain/utils/output_parsers/N8nOutputFixingParser.ts

@@ -39,7 +39,12 @@ export class N8nOutputFixingParser extends BaseOutputParser {
 
 		try {
 			// First attempt to parse the completion
-			const response = await this.outputParser.parse(completion, callbacks, (e) => e);
+			const response = await this.outputParser.parse(completion, callbacks, (e) => {
+				if (e instanceof OutputParserException) {
+					return e;
+				}
+				return new OutputParserException(e.message, completion);
+			});
 			logAiEvent(this.context, 'ai-output-parsed', { text: completion, response });
 
 			this.context.addOutputData(NodeConnectionType.AiOutputParser, index, [

packages/@n8n/nodes-langchain/utils/output_parsers/N8nStructuredOutputParser.ts

@@ -5,7 +5,7 @@ import type { ISupplyDataFunctions } from 'n8n-workflow';
 import { NodeConnectionType, NodeOperationError } from 'n8n-workflow';
 import { z } from 'zod';
 
-import { logAiEvent } from '../helpers';
+import { logAiEvent, unwrapNestedOutput } from '../helpers';
 
 const STRUCTURED_OUTPUT_KEY = '__structured__output';
 const STRUCTURED_OUTPUT_OBJECT_KEY = '__structured__output__object';
@@ -36,11 +36,14 @@ export class N8nStructuredOutputParser extends StructuredOutputParser<
 			const json = JSON.parse(jsonString.trim());
 			const parsed = await this.schema.parseAsync(json);
 
-			const result = (get(parsed, [STRUCTURED_OUTPUT_KEY, STRUCTURED_OUTPUT_OBJECT_KEY]) ??
+			let result = (get(parsed, [STRUCTURED_OUTPUT_KEY, STRUCTURED_OUTPUT_OBJECT_KEY]) ??
 				get(parsed, [STRUCTURED_OUTPUT_KEY, STRUCTURED_OUTPUT_ARRAY_KEY]) ??
 				get(parsed, STRUCTURED_OUTPUT_KEY) ??
 				parsed) as Record<string, unknown>;
 
+			// Unwrap any doubly-nested output structures (e.g., {output: {output: {...}}})
+			result = unwrapNestedOutput(result);
+
 			logAiEvent(this.context, 'ai-output-parsed', { text, response: result });
 
 			this.context.addOutputData(NodeConnectionType.AiOutputParser, index, [

packages/@n8n/nodes-langchain/utils/tests/helpers.test.ts

@@ -4,7 +4,7 @@ import { NodeOperationError } from 'n8n-workflow';
 import type { ISupplyDataFunctions, IExecuteFunctions, INode } from 'n8n-workflow';
 import { z } from 'zod';
 
-import { escapeSingleCurlyBrackets, getConnectedTools } from '../helpers';
+import { escapeSingleCurlyBrackets, getConnectedTools, unwrapNestedOutput } from '../helpers';
 import { N8nTool } from '../N8nTool';
 
 describe('escapeSingleCurlyBrackets', () => {
@@ -243,3 +243,101 @@ describe('getConnectedTools', () => {
 		expect(tools[0]).toBe(mockN8nTool);
 	});
 });
+
+describe('unwrapNestedOutput', () => {
+	it('should unwrap doubly nested output', () => {
+		const input = {
+			output: {
+				output: {
+					text: 'Hello world',
+					confidence: 0.95,
+				},
+			},
+		};
+
+		const expected = {
+			output: {
+				text: 'Hello world',
+				confidence: 0.95,
+			},
+		};
+
+		expect(unwrapNestedOutput(input)).toEqual(expected);
+	});
+
+	it('should not modify regular output object', () => {
+		const input = {
+			output: {
+				text: 'Hello world',
+				confidence: 0.95,
+			},
+		};
+
+		expect(unwrapNestedOutput(input)).toEqual(input);
+	});
+
+	it('should not modify object without output property', () => {
+		const input = {
+			result: 'success',
+			data: {
+				text: 'Hello world',
+			},
+		};
+
+		expect(unwrapNestedOutput(input)).toEqual(input);
+	});
+
+	it('should not modify when output is not an object', () => {
+		const input = {
+			output: 'Hello world',
+		};
+
+		expect(unwrapNestedOutput(input)).toEqual(input);
+	});
+
+	it('should not modify when object has multiple properties', () => {
+		const input = {
+			output: {
+				output: {
+					text: 'Hello world',
+				},
+			},
+			meta: {
+				timestamp: 123456789,
+			},
+		};
+
+		expect(unwrapNestedOutput(input)).toEqual(input);
+	});
+
+	it('should not modify when inner output has multiple properties', () => {
+		const input = {
+			output: {
+				output: {
+					text: 'Hello world',
+				},
+				meta: {
+					timestamp: 123456789,
+				},
+			},
+		};
+
+		expect(unwrapNestedOutput(input)).toEqual(input);
+	});
+
+	it('should handle null values properly', () => {
+		const input = {
+			output: null,
+		};
+
+		expect(unwrapNestedOutput(input)).toEqual(input);
+	});
+
+	it('should handle empty object values properly', () => {
+		const input = {
+			output: {},
+		};
+
+		expect(unwrapNestedOutput(input)).toEqual(input);
+	});
+});