DoppelAPI: The "Digital Twin" for Your Backend

Samet UCA — Mon, 02 Feb 2026 16:57:25 +0000

What I Built
I built DoppelAPI, a powerful CLI tool designed to solve the age-old bottleneck in software development: Frontend developers waiting for backend APIs to be implemented.

DoppelAPI takes your existing OpenAPI (Swagger) definition and instantly converts it into a fully functional, intelligent mock server. It creates a "Digital Twin" of your future backend, allowing teams to build, test, and integrate immediately.

Unlike standard mock servers that return static or empty data, DoppelAPI is intelligent:

Smart Data Generation: Instead of returning null or "string", it uses AI-driven Faker.js integration to generate realistic data (real names, UUIDs, avatars) based on your schema types.

Visual Dashboard: It launches a beautiful local web interface that serves as live documentation, showing precise JSON request bodies and response examples.

Chaos & Latency Simulation: It allows you to simulate "Real World" conditions. With flags like --delay (network lag) and --chaos (random server crashes), you can test how your app handles edge cases.

Postman Ready: One-click export of your entire mock API as a Postman Collection.

It transforms a static YAML file into a living, breathing API ecosystem.

Demo
You can find the source code and full documentation here: https://github.com/sametuca/doppelapi

Quick Start
You can run it instantly using the interactive wizard or command line arguments:

Bash

Install globally

npm install -g doppelapi

Run the wizard (Auto-discovers your OpenAPI files)

doppelapi

Or use specific flags

doppelapi start ./openapi.yaml --watch --delay --chaos
My Experience with GitHub Copilot CLI
Building DoppelAPI was an intense sprint, and GitHub Copilot CLI was my pair programmer throughout the entire process. It fundamentally changed how I approached CLI development.

Here is how Copilot CLI helped me build the specific features of DoppelAPI:

Building the "Chaos Mode" Logic I wanted a feature to simulate server instability. I asked Copilot CLI directly in the terminal:

"How can I write an Express middleware that randomly returns a 500 error 10% of the time to simulate server instability?"

It generated the exact math (Math.random() < 0.1) and middleware structure, which I instantly integrated into the --chaos flag logic.

Smart Data Mapping (Faker.js) Mapping complex OpenAPI types to Faker.js functions is tedious. I used Copilot to generate the mapping logic:

"Write a function that maps OpenAPI types like 'string', 'uuid', and 'email' to corresponding Faker.js methods."

This helped me implement the "Smart Data" feature where users can even use x-faker extensions in their schema.

Visual Dashboard & Postman Export Generating a Postman collection JSON from an OpenAPI object is complex. Copilot CLI helped me understand the structure required by Postman:

"Convert an OpenAPI path object into a Postman Collection item format using JavaScript."

This allowed me to build the "One-Click Export" feature that developers love.

Interactive CLI Wizard To make the tool user-friendly, I wanted an auto-discovery feature. Copilot guided me on how to use glob patterns to find .yaml files in the current directory and present them in a selection list.

Conclusion: GitHub Copilot CLI didn't just write code; it helped me design features. It acted as a bridge between my ideas (like "Chaos Mode") and the implementation, allowing me to build a production-grade tool in a fraction of the time.

Copilot cli usage phase

Developer Spawn Point - Portfolio

Samet UCA — Wed, 14 Jan 2026 21:50:28 +0000

This is a submission for the New Year, New You Portfolio Challenge Presented by Google AI

Exploring the Future: A 3D Cyberpunk Portfolio Powered by Gemini AI
About Me
Hi! I'm Samet Uca, a Full Stack Developer with a passion for pushing the boundaries of the web. I've always been fascinated by how we can transform traditional, flat web interfaces into immersive, interactive experiences.

I believe that a developer's portfolio should be more than just a list of links—it should be a window into their digital world. My "Living Space" is my creative sanctuary, and I wanted to express that through a 3D environment that feels personal, alive, and uniquely mine.

Portfolio

How I Built It
Building an immersive 3D environment requires a robust tech stack and a seamless development process. Here’s how I brought this vision to life:

🛠 Tech Stack
Frontend Framework: React 19 & Vite for a lightning-fast UI.
3D Engine: Three.js with @react-three/fiber and @react-three/drei for the 3D room and interactive models.
Styling: Tailwind CSS 4 for modern, utility-first styling.
Animations: Framer Motion for smooth UI transitions and overlays.
Google AI Integration
The core "intelligence" of this portfolio is powered by Google AI:

Antigravity: This entire project was developed within Antigravity, Google's AI-first development environment. The AI-native features allowed me to rapidly iterate on complex 3D mathematics and component structures, significantly reducing development time.
Gemini AI (1.5 Flash): I integrated the Gemini API directly into the portfolio via a feature I call the "Gemini Link". It’s a real-time, terminal-style interface where visitors can chat with an AI assistant that represents me, answering questions about my skills, experience, and projects in a witty, cyberpunk tone.
Google Cloud Run: The application is containerized and deployed on Cloud Run, ensuring it’s always fast, responsive, and ready to handle visitors globally.
The Living Space: A Reflection of Self
Why a 3D room? Because our living spaces are where our personalities truly live. Every object in this scene tells a story:

The Desk: My workspace, where code comes to life.
The Interactive Light Rig: A nod to my technical curiosity, allowing visitors to change the "vibe" of the room.
The Shelves: Representing the constant learning and different "layers" of my development journey.
By inviting you into this virtual room, I’m showing you not just what I build, but how I think and live as a creator.

What I'm Most Proud Of
I’m most proud of the Gemini Link Terminal. Integrating a large language model like Gemini into a 3D environment creates a bridge between visual immersion and interactive intelligence. Instead of just reading a static CV, visitors can talk to my digital twin.

I also put a lot of effort into the interactive 3D elements, such as the Google-themed light rig and the detailed developer desk. These small details aim to create a "personality-first" experience that standard portfolios often lack.

Built with ❤️ using Antigravity and Gemini.

DEV Community: Samet UCA

DoppelAPI: The "Digital Twin" for Your Backend

Install globally

Run the wizard (Auto-discovers your OpenAPI files)

Or use specific flags

Developer Spawn Point - Portfolio