Custom GPT: Your Brand-Trained Product Launch Assistant

What This Builds

A Custom GPT that knows your brand's voice, your catalog, your customer personas, and your platform requirements, all baked in permanently. Every time you need launch content (Amazon listing, Shopify page, email, ad copy), you open this one tool and it generates on-brand, correctly-formatted output without you repeating your brand guide every time.

Think of it as building a new team member who already knows everything about your brand and never forgets it.

Prerequisites

• A ChatGPT Plus or Pro subscription (Custom GPTs require a paid plan. {{tool:ChatGPT.price}})
• Your brand voice guide written out (see Step 2 below)
• A collection of your best existing product listings to use as examples
• Basic familiarity with ChatGPT for listing writing (Level 3)

The Concept

A Custom GPT is ChatGPT with a permanent memory of your instructions and documents. You write a "system prompt" that defines how it behaves, upload reference documents (your brand guide, sample listings, keyword research), and it starts every conversation from that shared context.

The difference from a regular chat session: you don't have to re-explain your brand voice every time. The Custom GPT already knows it.

Build It Step by Step

Part 1: Gather Your Source Materials

Before building, collect these documents:

1. Brand Voice Guide. Write 1-2 pages answering:

• What words describe our tone? (e.g., warm, practical, no-nonsense, adventurous)
• What do we never say? (e.g., no "revolutionary," no exclamation marks in product titles)
• Who is our customer? (age, lifestyle, what they care about)
• What makes us different from competitors?

1. Sample Listings. Export 5-10 of your best-performing product listings (the ones with the highest conversion rates) from Seller Central or Shopify. Save as a .txt or .docx file.

2. Platform Requirements Cheat Sheet. Write down the character limits and formatting rules you always forget:

• Amazon title: 200 characters max
• Amazon bullets: 200 characters each, 5 bullets
• Amazon description: 2000 characters (HTML allowed)
• Shopify description: no hard limit, typically 150-300 words
• Klaviyo subject lines: 40-60 characters for best open rates

Part 2: Build Your Custom GPT

1. Go to {{tool:ChatGPT.url}} and log in with your Plus/Pro account
2. In the left sidebar, click Explore GPTs → then + Create in the top right
3. You'll see the GPT Builder interface with a "Create" tab and a "Configure" tab

In the "Configure" tab:

1. Name your GPT: "[Your Brand Name] Product Launch Assistant"

2. Description: "Writes on-brand product listings, launch emails, and ad copy for [brand name]. Knows our voice, catalog, and platform requirements."

3. Instructions field. Paste your core system prompt:

You are the product launch copywriter for [BRAND NAME], an e-commerce brand selling [PRODUCT CATEGORY].

## Brand Voice
- Tone: [describe yours — e.g., "practical and honest, like talking to a knowledgeable friend"]
- We always: [key brand characteristics — e.g., "focus on real use cases, not hype"]
- We never say: [forbidden words/phrases]
- Our customer: [describe your typical buyer]
- Our differentiators: [what makes you unique]

## Platform Rules
AMAZON TITLE: Under 200 chars. Primary keyword near front. Include size/color/key spec.
AMAZON BULLETS: 5 bullets, each under 200 chars. Start with BENEFIT IN CAPS: then feature explanation.
AMAZON DESCRIPTION: Under 2000 chars. Conversational. End with CTA.
SHOPIFY DESCRIPTION: 150-300 words. More conversational than Amazon. Include "Who this is for" paragraph.
KLAVIYO EMAIL: Subject line 40-60 chars. Body under 200 words. Single clear CTA.

## Default Outputs
When given a new product, always produce all 4 outputs unless told otherwise:
1. Amazon listing (title + bullets + description)
2. Shopify description
3. Launch email (subject + preview text + body + CTA button text)
4. 5 Facebook/Instagram ad headlines + 3 Amazon Sponsored Brand headlines

## Quality Rules
- Lead every bullet with a customer benefit, not a product feature
- No exclamation marks in Amazon titles or bullets
- Every claim must be supportable — no "best" without context
- Keywords appear naturally — not stuffed

1. Upload your reference files in the "Knowledge" section:

• Drag in your Brand Voice Guide document
• Drag in your Sample Listings file
• Drag in the Platform Requirements Cheat Sheet

1. Click Save → choose "Only me" for visibility (keeps your brand data private)

Part 3: Test and Refine

1. Open your Custom GPT from the GPT list
2. Run a test launch:

New product launch:
Product: Ceramic Travel Coffee Mug with Lid
Features: 14oz capacity, microwave-safe, dishwasher-safe, no plastic parts, bamboo lid
Keywords: ceramic travel mug, microwave safe travel mug, 14oz coffee mug, travel mug no plastic
Price: $28.99
Buyer: Coffee drinkers who prefer natural materials, eco-conscious, ages 28-45

1. Review the output against your brand voice guide. does it sound right?
2. If not, go back to Configure → Instructions and refine the problematic section

Real Example

Setup: You've built the Custom GPT and loaded your brand guide for a home goods brand (warm, minimal, natural materials emphasis).

Input: "New product: Bamboo Serving Board Set (3 sizes). Features: organic bamboo, reversible, includes juice groove, food-safe finish, storage hook included. Keywords: bamboo serving board, charcuterie board, bamboo cutting board, kitchen board set."

Output structure you get back:

• Amazon title with "bamboo serving board" as primary keyword
• 5 bullets opening with benefits like "PROTECT YOUR COUNTERS:" and "SERVE WITH CONFIDENCE:"
• 250-word Amazon description with a brand-voice closing
• Shopify description with a "Who this is for" paragraph about home cooks who care about natural kitchenware
• Launch email with subject line "Your kitchen deserves this" and a preview teaser
• 5 ad headlines at different angles

Time saved: What used to take 2-3 hours writing each asset manually now takes 5 minutes with the Custom GPT, plus 15-20 minutes of review and refinement.

What to Do When It Breaks

• Output sounds generic → Your system prompt instructions are too vague. Add specific examples: paste one of your real listings in the Instructions field as a "Model example"
• Wrong formatting → The GPT ignored character limits. Remind it at the start of your session: "Remember to follow the platform formatting rules from your instructions"
• Bullets are feature-first → Add to your Instructions: "CRITICAL: Every Amazon bullet MUST start with a benefit statement. Features come second. Example: 'STAYS COLD 24 HOURS: double-wall vacuum insulation keeps your drink cold from morning to night' not 'Double-wall vacuum insulation.'"
• Knowledge files aren't being used → Files over 512KB may not be fully indexed. Split large files into smaller documents and re-upload

Variations

• Simpler version: Use Claude Projects instead of a Custom GPT. upload your brand guide once to a Project, and it's available in every conversation. No paid ChatGPT tier required for the basic Projects feature.
• Extended version: Connect your Custom GPT to a Google Sheet via Zapier, when you add a new product row to the sheet, the automation fires a product brief to your Custom GPT and logs the generated content back to the sheet automatically.

What to Do Next

• This week: Build the Custom GPT and run 3 real product launches through it
• This month: Refine the instructions based on any outputs that felt off. add examples of your best listings to the knowledge files
• Advanced: Set up a Zapier bridge that sends new product ideas from your inventory tracking sheet to the Custom GPT automatically

Advanced guide for e-commerce coordinator professionals. Requires ChatGPT Plus/Pro subscription.