Build a Custom GPT with Actions and Knowledge

Custom GPTs let you package instructions, documents, and API calls into a reusable assistant. This tutorial covers the advanced setup.

Prerequisites

• ChatGPT Plus or Team
• A clear use case (e.g., support bot, research assistant, internal tool)

Step 1: Define the GPT

Create a new GPT. In the instructions, include: role, tone, constraints, and output format. Example: "You are a B2B support assistant. Answer only from the knowledge base. If unsure, say so. Never make up product details."

Step 2: Upload knowledge

Add PDFs, docs, or text files. The GPT will use them for context. Keep files focused—too much dilutes relevance. Update when your docs change.

Step 3: Add actions (optional)

Actions let the GPT call external APIs. You define an OpenAPI spec: endpoints, parameters, auth. The GPT decides when to call based on the conversation. Use for: lookup data, create tickets, search your DB.

Step 4: Configure capabilities

• Web browsing – For research GPTs that need current info.
• Code interpreter – For math, data, or file analysis.
• Image generation – If you need DALL·E in the flow.

Step 5: Test and iterate

Try edge cases: out-of-scope questions, ambiguous requests, adversarial inputs. Refine instructions until behavior is consistent.

Deployment

Share with your org (private) or publish (public). For sensitive data, use the Team plan and restrict sharing.