Backend Engineer

About Entry Cell

Entry Cell is a small, fast-moving team focused on building, operating, and scaling AI-powered products in real production environments.

We do not stop at prototypes.

We take responsibility for stability, cost, latency, and long-term maintainability.

Our work includes AI chatbots (text and real-time voice), Ads SDKs, and internal automation systems.

This role is for engineers who are comfortable owning problems end-to-end, not just implementing assigned tasks.

What You Will Do

• Own AI features from design to deployment and long-term operation
• Build and operate AI chatbots and automation features used by real users
• Design services using external LLM APIs such as OpenAI and Anthropic
• Make practical trade-offs between quality, latency, cost, and failure modes
• Design prompts, session handling, rate limits, caching, and model switching strategies
• Develop and maintain Ads SDK with production traffic and real releases
• Improve system architecture and reduce technical debt over time
• Proactively identify problems worth solving beyond assigned tasks
• Run experiments, share results, and raise the team's technical standards

Minimum Qualifications

• Experience launching and operating real services in production
• Strong AI-assisted coding skills using tools like Claude, Codex, or Copilot
• Ability to verify, refactor, and take responsibility for AI-generated code
• Hands-on experience with LLM APIs such as OpenAI or Anthropic
• Experience dealing with cost issues, failures, or quality problems is a plus
• Broad technical understanding across backend, APIs, deployment, and testing
• Comfort working beyond a single technical specialty when needed
• High level of technical independence in debugging and problem-solving
• Strong sense of ownership and initiative

Preferred Qualifications

• Experience with prompt engineering, RAG, MCP, or LLM Prompt Engineering
• Experience with multiple programming languages such as Rust, , PHP or Python
• Habit of documenting experiments and sharing technical learnings
• Korean language ability is a plus, but not required

Who We Are Looking For

• Someone who does not just use AI, but builds systems that survive AI in production
• Someone who notices cost spikes, latency issues, or brittle architecture and investigates immediately
• Someone who focuses on what will move the product forward, not only what was asked

Work Environment

• Remote-first team
• Work from anywhere globally
• English-only communication is fully supported
• Korean speakers are welcome, but Korean is not required

Entry Cell values autonomy, trust, and real ownership.

If you enjoy building AI systems that actually run in the real world, we would love to talk.