How I Built a Custom Pega DX Component Using Claude Code — Step by Step
If you’ve ever wanted to build a custom DX component for Pega Constellation but got halfway through the documentation and quietly closed the tab — this one’s for you. I recently built a FEIN Masked Input component using Claude Code, and what used to take a couple of days took me an afternoon. Here’s exactly how I did it, so you can replicate it.
What I Built
A custom Field component that masks a FEIN (Federal Employer Identification Number) and displays only the last 4 digits — with three rendering modes: edit, read-only, and display-only.
My Environment Setup
I installed the following on my windows laptop:
- VSCode — (my IDE of choice)
- Git
- Claude Extension for VSCode
- Node.js + NPM
If you already have VSCode and Git, you’re halfway there.
Step 1 — Give Claude the Pega Playbook
This is the move that makes everything else work. Instead of asking Claude to figure out Pega DX conventions from scratch — you point it at Pega’s own implementation.
Download the Pega Constellation UI Gallery from GitHub: GitHub - pegasystems/constellation-ui-gallery: This open-source repository provides a collection of ready-to-use and customizable Constellation DX components. Use this resource to gain inspiration, best practices, and a solid foundation for implementing custom components. · GitHub
Claude will run through the entire repository — all 1,500+ lines of documentation, all 53 components — and build a comprehensive internal knowledge base. This takes a few minutes. Get a coffee. When you come back, Claude will have a markdown file, I called it GUIDE.MD that serves as your project reference for every future component you build.
Step 2 — Ask Claude to Build Your Component
Once Claude has ingested the gallery, building a component is a conversation. I typed:
“I want a field that masks FEIN and only shows the last 4 digits.”
That’s it. No boilerplate, no config hunting, no figuring out which Cosmos primitive to use. Because Claude already knows the entire gallery, it:
- Identified the correct component type (Field / Text subtype)
- Found the closest reference implementation (MaskedInput)
- Generated all required files: index.tsx, config.json, Docs.mdx, demo.stories.tsx, demo.test.tsx
- Handled all three rendering modes (edit, read-only, display-only)
- Applied the correct prop patterns, coercions, and API calls
Step 3 — Build and Publish
When I asked how to build and publish, Claude gave me the exact four commands in order
npm run lint # Validate code quality
npm run buildComponent # Bundle your component
npm run authenticate # Connect to your Pega server
npm run publish # Ship it as a Rule-UI-Component
A few things to configure before you run these:
- Edit tasks.config.json with your Pega server URL, ruleset name, ruleset version, and OAuth client credentials
**Tip – If you do not have the keys you can use “ClientCreds” as the grantType to make it work. Always follow the recommended pattern for your organization.
- Make sure your constellation-ui-gallery folder is your working directory
**Note – I ran into errors running npm commands, every time I encountered an error, I put the error back into Claude to guide me. With its help I was able to move forward.
Step 4 — Use It in Pega
Open App Studio and your component appears in the Library under DX Components. Make sure it is selected. Once done you are ready to use it.
In my case I created a simple text property and when I added it to my view, in the configure field option (clicking the gear) under “Display as” you could see the FEIN Input Mask. I chose it. The FEIN Masked Input masked the identifier correctly on entry and displayed only the last four digits in read-only mode. Exactly as specified.
Tips From My Experience
-
Commit your markdown file (Guide.md in my case) to Git after Claude generates it. It becomes the context anchor for every future conversation — just tell Claude to “read the Guide” at the start of a new session and it’s back up to speed instantly.
-
Be specific in your prompts. “A field that masks FEIN and shows the last 4 digits” gets better output than “a masked input field.” The more you describe the business requirement, the better Claude matches it to the right pattern.
-
Check tasks.config.json before you publish. The most common first-publish failure is a missing or incorrect OAuth client ID. Claude will tell you exactly what to fill in if you ask.
The Bottom Line
The Pega DX component framework is powerful but has some learning curve if you approach it cold. Pairing Claude Code with the Constellation UI Gallery effectively gives you an expert co-developer who has already read everything, remembers everything, and is available when you need them.
Give it a try and share what you build.
Enjoyed this article?
See suggested articles from our Constellation 101 series and view all our Knowledge Shares from our User Experience Expert Circle.
