How to Prepare for a Technical Phone Screen

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The technical phone screen sits between the recruiter call and the on-site coding rounds. A senior engineer calls you for 30 to 45 minutes and asks about your technical background — no code editor, just a conversation. It is deceptively difficult because you cannot hide behind syntax. You have to actually explain how things work.

This guide covers what a technical phone screen looks like, what topics come up, how to talk about your projects, and how to prepare effectively.

What a technical phone screen looks like

The interviewer is typically a senior engineer or engineering manager. They have your resume in front of them. The conversation usually follows this pattern:

Warm-up (2-3 minutes). Brief introductions. The interviewer explains the format.
Resume deep-dive (10-15 minutes). They pick a project from your resume and ask you to walk them through it. Then they dig into the technical details: "Why did you choose Postgres over Mongo?" "How did you handle caching?" "What would you change if you rebuilt it?"
Technical concepts (10-15 minutes). Broader questions about fundamentals: "How does HTTPS work?" "What happens when you type a URL in a browser?" "Explain the difference between SQL and NoSQL databases."
Your questions (5 minutes). The interviewer asks if you have questions about the team or company.

The exact mix varies. Some interviewers spend the entire time on your projects. Others focus more on fundamentals. The one constant: they follow your lead. If you mention Redis, they will ask about Redis. If you mention microservices, they will ask about service discovery.

The most common topics

Your projects and technical decisions

This is the most important category. For every project on your resume, you should be able to explain:

The problem it solved and why it mattered
The architecture at a high level (what talks to what)
Your specific contributions (not the team, you)
Key technical decisions and why you made them
What you would do differently with hindsight
Scale: how many users, requests per second, data volume

The "what would you change" question is almost guaranteed. Having a thoughtful answer shows you are reflective about your work, not just building and moving on.

System design basics

You will not design a full system in a phone screen, but you should be comfortable discussing:

Load balancing and horizontal scaling
Caching strategies (CDN, Redis, in-memory)
Database choices and tradeoffs (SQL vs NoSQL, indexing)
API design (REST vs GraphQL, versioning, pagination)
Message queues and async processing
Monitoring, logging, and observability

Web fundamentals

For web-focused roles, expect questions about:

HTTP methods, status codes, headers
Authentication and authorization (JWT, OAuth, sessions)
CORS and security basics (XSS, CSRF)
Browser rendering pipeline
CSS layout (flexbox, grid) and responsive design
Performance optimization (lazy loading, code splitting, caching)

Language and framework depth

If your resume lists a language or framework, you are fair game for deep questions. Common examples:

React. Virtual DOM, reconciliation, hooks lifecycle, state management patterns, server components
Node.js. Event loop, streams, clustering, memory management
Python. GIL, generators, decorators, async/await
Java. JVM internals, garbage collection, concurrency primitives

The rule of thumb: do not list anything on your resume that you cannot discuss for 5 minutes. If you used a technology once in a hackathon, leave it off.

How to talk about your projects

Most candidates make one of two mistakes: they either give a 30-second summary that is too shallow, or they launch into a 10-minute monologue that loses the interviewer. Here is a better structure:

The 60-second overview

Start with a concise overview: what the project does, who uses it, and what your role was. The interviewer will guide you from there.

"I built the real-time notification system for our e-commerce platform. It handles about 50,000 events per minute — order updates, shipping alerts, price drops. I designed the architecture and implemented the core pipeline using Kafka and WebSockets."

Notice: specific numbers, clear scope, and what you personally did. This gives the interviewer multiple threads to pull on — they might ask about Kafka, WebSockets, scaling, or the event schema.

Anticipate the follow-ups

For each project, prepare answers to these follow-ups (they are almost guaranteed):

"Why did you choose [technology X] over alternatives?"
"What was the hardest part?"
"How did you handle [edge case / failure mode]?"
"How would you scale this 10x?"
"What would you do differently?"

Be honest about gaps

If you do not know something, say so. "I am not sure how Kafka handles exactly-once delivery — I used at-least-once in my implementation with idempotent consumers." That answer shows more technical maturity than guessing.

Common mistakes

Listing technologies without depth. Saying "I used React, Node, Postgres, Redis, and Docker" tells the interviewer nothing. They will ask about whichever one they know best, and you need to go deep.
Not knowing your own resume. If it has been a year since you worked on a project, review it before the interview. Interviewers notice when you struggle to remember your own work.
Saying "we" for everything. Team projects are fine, but the interviewer is evaluating you. Be clear about what you personally designed, built, or decided.
Getting defensive. When an interviewer challenges your technical decision, they are testing how you think — not attacking you. Engage with the alternative they suggest and explain your reasoning.

How to practice

The best practice for technical phone screens is simulating the actual conversation. Reading about system design helps, but the real skill is articulating your knowledge verbally under time pressure.

AI technical phone screen practice simulates this exactly. An AI senior engineer asks about your projects, digs into technical details, and pushes for specifics — so you can identify weak spots before the real interview.

If you prefer self-study, try this exercise: pick a project from your resume, set a 2-minute timer, and explain it out loud as if an interviewer asked "walk me through this." Record yourself and listen back. You will immediately notice where you ramble, where you lack detail, and where the explanation breaks down.

Bottom line

Technical phone screens test whether you truly understand the technologies you have worked with. You cannot cram for them the way you can for coding interviews. The preparation is ongoing: know your resume inside and out, understand the fundamentals behind your technology choices, and practice explaining complex ideas clearly over voice. If your resume is honest and you can go deep on 2 to 3 projects, you are in good shape.

Once you are comfortable with the technical screen, prepare for the coding round next. And if behavioral questions are on your radar, read our behavioral interview questions guide for a complete list of common questions with STAR examples.

Frequently asked questions

What is the difference between a technical phone screen and a coding interview?

A technical phone screen is a conversation about your technical experience, projects, and knowledge. There is no code editor. A coding interview involves solving an algorithm or data structure problem in a live editor while explaining your approach. They test different skills.

How long does a technical phone screen last?

Most technical phone screens last 30 to 45 minutes. The interviewer usually spends the first few minutes on introductions, then 20 to 30 minutes on technical questions, and leaves time at the end for your questions.

What topics should I review for a technical phone screen?

Focus on whatever is on your resume. If you listed React, be ready to explain the virtual DOM, hooks, and rendering lifecycle. If you listed distributed systems, know about CAP theorem, load balancing, and caching. Also review fundamentals: HTTP, databases, API design, and basic system design.