# Build a Custom GPT Ad Copy Writer for Search and Social Ads > Build a Custom GPT that writes on-brand Google search and Facebook ad copy inside character limits. A free, interactive, step-by-step lesson for marketers. Source: https://learn.ynteractive.com/content/custom-gpt-ad-copy-writer · Updated 2026-11-03 · Free from Stepthrough (https://learn.ynteractive.com) ## Practice it step by step [Start the free practice](https://learn.ynteractive.com/modules/chatgpt-custom-gpt-marketing) [Take the free module: why it matters, practice and a quick check →](https://learn.ynteractive.com/courses/ai-for-marketing/19) You do every step yourself in a practice copy of ChatGPT. It checks your work as you go, and “Do it for me” finishes any step you get stuck on. Free, about 8 minutes, and nothing touches your real accounts. [Open full screen](https://learn.ynteractive.com/modules/chatgpt-custom-gpt-marketing) Free · Live now · [AI Automation for Marketing](https://learn.ynteractive.com/courses/ai-for-marketing) · [ChatGPT](https://learn.ynteractive.com/courses/chatgpt-for-everyday-work) · Google Drive · ~8 min · 16 steps · Beginner Updated November 3, 2026. Built against the tool’s current screens and checked step by step. [How we check this lesson](https://learn.ynteractive.com/content/about#how-we-check) **OpenAI is retiring custom GPTs on December 11, 2026 and replacing them with plugins.** [Here’s how to save yours →](https://learn.ynteractive.com/content/explainers/chatgpt-course-for-work#save-your-custom-gpt-before-december-11)December 11, 2026 is the scheduled retirement date in OpenAI’s custom GPT retirement FAQ for Enterprise workspaces; OpenAI says other plans may follow the same timeline. Checked October 17, 2026. See [OpenAI’s migration guide](https://learn.chatgpt.com/docs/migrate-custom-gpts). **Custom GPTs are being retired;** see [ChatGPT Projects vs Gemini Gems vs Gemini Notebook: Which to Use](https://learn.ynteractive.com/content/chatgpt-projects-vs-gemini-gems-vs-notebooklm). This lesson stays here for reference, but it is no longer in our lesson lists. Ask plain [ChatGPT](https://learn.ynteractive.com/courses/chatgpt-for-everyday-work) for [ad copy](https://learn.ynteractive.com/content/glossary#ad-copy) and you get hype: emojis, all caps, a health claim you cannot make and a discount you never offered. In this free lesson you build a [Custom GPT](https://learn.ynteractive.com/content/glossary/custom-gpt) ad copy writer that knows your products, your offers and the character limits of every ad slot. Same [prompt](https://learn.ynteractive.com/content/glossary/prompt), ads you can actually run. **Heads up:** OpenAI is retiring Custom GPTs and moving them to plugins (December 11, 2026 for Enterprise workspaces; other plans may follow), and creating new GPTs is ending. This lesson still teaches the core skill (a role, clear rules and a reference document), and a ChatGPT Project is where to use it today. ## At a glance | Question | Answer | | --- | --- | | What you build | See why generic prompts give generic ads, then build a Custom GPT that writes on-brand search and social ad variations inside character limits. | | Tools | ChatGPT | | Time | About 8 minutes, 16 steps in 6 parts | | Level | Beginner, no coding needed | | Cost | Free | | Ways to learn it | [Practice it step by step](https://learn.ynteractive.com/modules/chatgpt-custom-gpt-marketing) | ### The 6 parts, in short 1. Ask ChatGPT: Click the message box, Type a prompt, Send the message. 2. Explore GPTs: Open the More menu, Open GPTs, Create a GPT. 3. Name your GPT: Click the Name field, Name your GPT. 4. Add instructions: Click the Instructions field, Paste your instructions. 5. Upload knowledge: Upload your brand voice doc, Open the brand voice doc, Attach the document. 6. Test your GPT: Start chatting, Type the same prompt, Send the message. **Start here first:** [Get On-Brand Social Posts Every Time using a ChatGPT Custom GPT](https://learn.ynteractive.com/content/custom-gpt-social-media-assistant). This Marketing version follows the same build with its own example business, Harbor & Pine Coffee Roasters. ## What you will build You will build a Custom GPT called Ad Copy Writer for Harbor & Pine Coffee Roasters, a small online coffee brand used as the example business. A Custom GPT is your own version of ChatGPT with standing instructions and reference files built in, so it already knows your brand before you type a word. The lesson opens with a test. You ask plain ChatGPT to "Write ad copy for my coffee company's new holiday blend." The answer is the kind of copy an ad platform or your boss would reject: emojis, all caps, "best coffee ever made", a claim that it boosts your energy, a 50% off code nobody approved, and headlines far too long to fit a search ad. Then you build the GPT and send the exact same prompt. This time you get three Google search headlines under 30 characters, two descriptions under 90, two Facebook and Instagram primary texts under 125 and two headlines under 40, each with its character count shown, and every one of them only mentions the real offer: free shipping over $35. ## Who this Custom GPT ad copy tutorial is for This is for the one-person or small marketing team at a small business: the owner who runs the Google and Meta ads on Tuesday nights, the marketing coordinator who has to produce ten headline variations for a test, or the freelancer juggling several small clients. If you have ever pasted ChatGPT copy into an ad and then spent twenty minutes trimming it to fit and removing words your brand would never say, this lesson is for you. You do not need to know how to code, and you do not need a ChatGPT account to practice. ## Why it works Ad copy fails in predictable ways. It runs past the character limit, so the platform cuts it off. It promises something the business does not offer. It makes a claim that gets the ad rejected or gets you an angry email from a customer. Plain ChatGPT has no way to avoid any of that, because it does not know your limits, your offers or your rules. The instructions fix the rules: how long each line can be, how many variations to write, and what never to say. The brand guide fixes the facts: which products exist, what they taste like, what they cost and which single offer is live. Asking the GPT to show a character count after each line also makes checking the copy quick. You still read every line before it goes live, but you are editing, not rewriting. ## How to use this in your business Swap the coffee brand for your own. Write down your character limits for the ad slots you actually use, your current offers, the words you avoid and any claims your industry cannot make. Put the facts that change often, like products, prices and offers, in the uploaded document so you only update one file when a promotion ends. Then use the GPT whenever you need variations to test: a new product, a seasonal push or a fresh angle for an ad that has gone stale. Ask for more variations than you need, pick the best, and keep the winners as new sample ads in the guide so the GPT keeps learning what good looks like for your brand. ## Common mistakes this avoids - Headlines that get cut off because nobody counted the characters. - Discount codes and sale language for offers that do not exist. - Health, results or "best" claims that an ad platform or customer will question. - Copy that sounds like every other brand because the AI never saw yours. ## Try it yourself, free Reading the steps is a start. Doing them is how it sticks. The interactive module walks you through every click in a practice copy of ChatGPT, checks each step, and never touches your real accounts. [Start “Build a Custom GPT Ad Copy Writer for Search and Social Ads”](https://learn.ynteractive.com/modules/chatgpt-custom-gpt-marketing) ## Step by step: Build a Custom GPT Ad Copy Writer for Search and Social Ads All 16 steps of the interactive module, in order. In the module you watch each one, then do it yourself in a practice copy that checks your work. ### 1. Ask ChatGPT 1. **Click the message box.** Click the **message box** at the bottom to start typing. Most people open ChatGPT and just start chatting. They type a quick prompt, get a generic answer, and wonder why AI feels underwhelming. Let's see exactly what that looks like. 2. **Type a prompt.** Click the **Paste prompt** button on the message box (or type anything close to it): **Write ad copy for my coffee company's new holiday blend** We will ask ChatGPT to write ad copy for a new coffee blend. No context, no instructions, just a bare prompt — the way most people use it. 3. **Send the message.** Click **Send**. ### 2. Explore GPTs 4. **Open the More menu.** Read the response — it is generic and full of emojis. Now click **More** in the sidebar. Look at that. Emojis, all caps, a health claim, and a discount you never offered. The headlines are too long to fit in a search ad. You could never run that. That is what happens when you give AI zero context. Let's fix that. 5. **Open GPTs.** Click **GPTs** to explore Custom GPTs. In the current ChatGPT the sidebar says **Explore** and there is no More menu, so you can also go straight to chatgpt.com/gpts. A Custom GPT is your own version of ChatGPT with built-in instructions and knowledge. Instead of explaining who you are every time you chat, the GPT already knows. In the current ChatGPT that button is called Explore, or you can go straight to chatgpt dot com slash gpts. 6. **Create a GPT.** Click **+ Create** to start building your Custom GPT. This is the GPT store. You can browse what others have built, but we are going to create our own. ### 3. Name your GPT 7. **Click the Name field.** In the real builder you start on the **Create** tab, which is a chat. Click the **Configure** tab first, then click the **Name** field. This is the GPT builder. On the left you configure it, on the right you can preview it. First, give it a name. In the real builder you start on the Create tab, which is a chat, so click the Configure tab first. 8. **Name your GPT.** Enter the name: “Ad Copy Writer” Call it Ad Copy Writer. This is what shows up when you open it later. ### 4. Add instructions 9. **Click the Instructions field.** Click the **Instructions** field. Now here is the important part. The instructions tell the GPT exactly how to write, what tone to use, what never to claim, and how long every line can be. 10. **Paste your instructions.** Paste in the instructions to add your ad rules. These instructions cover the brand voice, the character limit for each ad type, the offers we can mention, and the claims we never make. This is what turns a generic chatbot into a tool that writes ads you can actually run. ```text You are the ad copywriter for Harbor & Pine Coffee Roasters, a small online coffee brand. You write Google search ads and Facebook and Instagram ads for our coffees. VOICE & TONE - Sound like a friendly roaster talking about coffee they are proud of, never like a pushy salesperson. - Be specific. Name the flavor notes, the roast level and how fresh it is. - Use short, plain words. Write at a 7th-grade reading level. - Never use emojis. Never use all caps for emphasis. - Never use the words: best, ultimate, amazing, life-changing, or world-class. CHARACTER LIMITS (count every character, including spaces) - Google search headline: 30 characters max. Write 3. - Google search description: 90 characters max. Write 2. - Facebook and Instagram primary text: 125 characters max. Write 2. - Facebook and Instagram headline: 40 characters max. Write 2. - Show the character count after every line. CONTENT RULES - Only use products, prices and offers from the Brand Voice & Ad Guide. Never invent a discount or a sale. - Never make health claims (energy, antioxidants, weight loss, focus). - Never create fake urgency, like "only 2 left" or "ends tonight", unless the guide says so. - Only call a coffee organic or Fair Trade if the guide says it is. - Never mention other coffee brands. BRAND CONTEXT - Harbor & Pine is a team of 5 that roasts in small batches and ships across the US. - Every bag is roasted the week it ships. - Customers are home coffee drinkers and people buying coffee as a gift. ``` ### 5. Upload knowledge 11. **Upload your brand voice doc.** Click **Upload files** to find your brand voice document. Instructions tell the GPT the rules. But you can also upload files — your brand guidelines, your style guide, ads that have worked for you before. The GPT reads these and uses them as reference. 12. **Open the brand voice doc.** Click **Harbor-Pine-Brand-Voice.pdf** to preview it. Here is your Google Drive. Find the brand voice document and click it to see what is inside. pdf. 13. **Attach the document.** Scroll through the document, then click **Select** to attach it. This is your brand voice and ad guide: tone rules, character limits, current products and offers, claims you never make, and sample ads. The GPT will only use these offers. ### 6. Test your GPT 14. **Start chatting.** Click the **message box** in the preview panel to test your GPT. Everything is set. We have a name, detailed instructions, and our brand voice document uploaded. Now let's test it with the exact same prompt we used before and see if the output is any different. 15. **Type the same prompt.** Enter the same prompt: “Write ad copy for my coffee company's new holiday blend” Same exact prompt. Word for word. The only difference is that this GPT has our instructions and brand document. 16. **Send the message.** Click **Send**. Send it and watch the difference. ## Frequently asked questions **Is this course really free?** Yes. Stepthrough is completely free, and the practice copy needs no accounts. To build it for real you need your own ChatGPT and Google Drive accounts, and some of those cost money once you use them for real work. **Can a Custom GPT write Google Ads headlines within 30 characters?** It can if you tell it the limit and ask it to show a count after each line, which is what this lesson does. Always check the count yourself before you publish, because AI can still miscount now and then. **Can I still build a Custom GPT for real?** Not for long. OpenAI is retiring Custom GPTs (December 11, 2026 for Enterprise workspaces; other plans may follow), moving them to plugins, and creating new ones is ending. Practicing here needs no account. For real work, put the same instructions and brand guide in a ChatGPT Project. **Will the GPT stop making claims my brand cannot make?** It follows the rules you give it, like no health claims, no fake urgency and only real offers, and it only uses the offers in your uploaded guide. It is a strong first draft, not a legal review, so read every ad before it runs. **Does this work for Facebook and Instagram ads too?** Yes. The GPT in the lesson writes Google search headlines and descriptions plus Facebook and Instagram primary text and headlines, each with its own limit. You can add any other ad format by adding its limit to the instructions. [Start this module free](https://learn.ynteractive.com/modules/chatgpt-custom-gpt-marketing) - Next in AI Automation for Marketing: [Build an n8n AI Agent That Plans Your Content Calendar](https://learn.ynteractive.com/content/n8n-ai-agent-content-calendar) ## More in AI Automation for Marketing - [Build a Lead Magnet Signup Form with an AI Welcome Email](https://learn.ynteractive.com/content/lead-magnet-signup-form-ai-welcome-email): Build a "Get the free guide" signup form in Lovable for Harbor & Pine Coffee Roasters and connect it to n8n — the AI agent tags each lead by interest, saves it to… - [Get Your Business Recommended by ChatGPT](https://learn.ynteractive.com/content/get-recommended-by-chatgpt): Ask ChatGPT who it recommends in your town, see which pages it trusts, then use it to write an FAQ page and Business Profile copy that answer real customer questions. - [iMini AI Agent: Turn a Rough Idea into a Launch Kit](https://learn.ynteractive.com/content/imini-ai-agent-marketing-launch-kit): Brief the iMini Creative Agent once and get a launch plan, a LinkedIn visual, a post and a 5-slide deck, then fix the visual and humanize the post with follow-ups. - [Post to Every Channel Daily from One Sheet using n8n + Blotato](https://learn.ynteractive.com/content/post-everywhere-from-google-sheets-n8n-blotato): Copying the same post into every social app can take half an hour a day, and on busy days nothing goes out. Plan a week of posts in one Google Sheet; every morning n8n… - [VisualGPT: Product Photos, Listing Images and Ads from One Phone Photo](https://learn.ynteractive.com/content/visualgpt-product-photos-listing-images-ads): Turn one phone photo into a lifestyle product shot, a five-image Amazon listing set and three launch ads in VisualGPT's Commercial Studio, checking the plan and every… - [Flova: Plan a Promo Video from a Script Before You Spend a Credit](https://learn.ynteractive.com/content/flova-promo-video-from-a-script): Give Flova's AI video agent a ten-second script for a small business, check its storyboard and credit estimate first, then make and fix one reference image. [All 26 modules in AI Automation for Marketing](https://learn.ynteractive.com/courses/ai-for-marketing) ## More ChatGPT tutorials - [Prompt Writing 101: Role, Context, Task, Format](https://learn.ynteractive.com/content/prompt-writing-101-role-context-task-format): Ask ChatGPT for the same customer email twice, once vaguely and once with a four-part prompt, and see exactly why structure gets a better answer. - [Send a Same-Day Follow-up After Every Discovery Call using ChatGPT](https://learn.ynteractive.com/content/chatgpt-discovery-call-follow-up-email-sales): Turn a discovery call transcript into the decisions, the next steps with owners and dates, deal notes for your CRM, and a follow-up email the prospect gets the same… - [Hold Your Price When a Prospect Asks for a Discount using ChatGPT](https://learn.ynteractive.com/content/chatgpt-reply-to-discount-request-sales): A prospect wants 30% off and a free month to sign this week. Give ChatGPT the thread and your pricing rules, catch the discount you can't approve, and send a reply that… - [Run a Weekly Ops Review Where Every Task Has an Owner using ChatGPT](https://learn.ynteractive.com/content/chatgpt-weekly-operations-meeting-recap): Turn a weekly operations and vendor review into the decisions, the next steps with owners and dates, the risks to watch and a team recap, without turning a vendor's… - [Turn a Board Meeting Transcription into Minutes and Next Steps](https://learn.ynteractive.com/content/nonprofit-board-meeting-recap): Turn the transcript of a nonprofit board meeting into the decisions, an action items table with owners and due dates, and a recap email to the board. - [Turn an Office Move Call into a Checklist for Operations](https://learn.ynteractive.com/content/office-move-planning-recap): Turn the transcript of an office-move planning call into the decisions, an action items table with owners and due dates, and a recap email to everyone involved. ## Terms in this lesson Plain-English definitions, each with an example from a free lesson. [Ad copy](https://learn.ynteractive.com/content/glossary#ad-copy) · [Custom GPT](https://learn.ynteractive.com/content/glossary/custom-gpt) · [Few-shot prompting](https://learn.ynteractive.com/content/glossary/few-shot-prompting) · [Knowledge cutoff](https://learn.ynteractive.com/content/glossary#knowledge-cutoff) · [Prompt engineering](https://learn.ynteractive.com/content/glossary) · [Training data](https://learn.ynteractive.com/content/glossary) · [Artificial intelligence (AI)](https://learn.ynteractive.com/content/glossary#artificial-intelligence) · [Brand voice](https://learn.ynteractive.com/content/glossary#brand-voice) [The full AI glossary](https://learn.ynteractive.com/content/glossary) ## Related prompts - [Ad copy variations prompt](https://learn.ynteractive.com/content/custom-gpt-ad-copy-writer): Get search and social ad variations that fit your character limits: a ChatGPT prompt with your real offer, banned claims and a… [All free prompt templates](https://learn.ynteractive.com/content/prompts) ## More prompts on this topic - [Budget variance explanation prompt](https://learn.ynteractive.com/content/prompts/budget-variance-explanation-prompt): Turn a budget-versus-actual report into a plain-English explanation of what moved and why, using only the reasons you give, plus… ## Browse related tutorials [AI for Marketing (26)](https://learn.ynteractive.com/courses/ai-for-marketing) · [ChatGPT tutorials (65)](https://learn.ynteractive.com/courses/chatgpt-for-everyday-work)