Automate LLM Testing with GPT-4 Judge & Google Sheets Tracking

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Built by Adam Janes Adam Janes
Created on June 05, 2026

Description

How it works
The workflow loads a list of test cases from a Google Sheet (previous results stored from an LLM)
For each test case, we execute a call to an LLM judge in parallel (using HTTP Request + Webhook nodes)
The judge uses the Input, Output, and Reference Answer fields from the spreadsheet to mark each LLM response as Pass/Fail
The results are logged into a separate sheet in the same Sheets file.

Set up steps:
Add your credentials for Google Sheets and OpenRouter (or replace the OpenRouter node with your favourite chat model).
Make a copy of the example Sheet to populate it with you own test data.
Run the workflow with the Execute Workflow button next to the Manual Trigger node.

Nodes Used (5)

Basic LLM Chain
@n8n/n8n-nodes-langchain.chainLlm
Google Sheets
n8n-nodes-base.googleSheets
HTTP Request
n8n-nodes-base.httpRequest
OpenRouter Chat Model
@n8n/n8n-nodes-langchain.lmChatOpenRouter
Structured Output Parser
@n8n/n8n-nodes-langchain.outputParserStructured