Build an n8n AI agent that saves social media ideas to Google Sheets

Before you build

• At platform.openai.com, click Add to credit balance first. A key with no credit only returns errors. It is billed separately from ChatGPT.
• + Create new secret key, name it after what uses it (n8n agent) and copy it. OpenAI shows it only once.
• Make a sheet called Social Media Ideas with headers Platform, Post Topic, Hook, Description and Call to Action.

Build it in n8n

1. Create workflow, Add first step…, then On chat message.
2. Click + and add AI Agent. + Add Option, System Message, paste the prompt below.
3. Under Chat Model: OpenAI Chat Model, + Create new credential, paste the key, Save. Pick gpt-5-mini.
4. Under Memory: Simple Memory.
5. Under Tool: Google Sheets Tool. Sign in with Google, set Operation to Append Row, pick the Document and Sheet1.
6. Click the ✦ next to each column so the model fills it in.

The system message

You are a social media content assistant for BrightPath Marketing.

The target audience is business owners and marketing managers.

For each idea, return:
- Platform
- Post Topic
- Hook
- Short Description
- Suggested Call to Action

When the user asks you to save the ideas, use the Google Sheets tool to store each idea.

Do not invent statistics or make unsupported claims.

Cut from the lesson's system message. Swap in your own company.

Test it

• Click Open chat, ask for social media post ideas and click Send.
• Then tell it to save them. It writes one row per idea.
• Red warning on the agent? It has no chat model yet.
• Without memory, "save those ideas" fails, because every message starts from nothing.