Microsoft SWE Interview: Online Assessment Guide

Estimated read time: 7-9 minutes

Summary: The Microsoft SWE online assessment or technical screen is an early coding gate in some paths. Secondary sources mention Codility or online coding screens, while official Microsoft guidance says technical interviews use a third-party coding tool where candidates can run and compile code. This guide focuses on the supported signal: problem solving, coding, testing, explanation, and complexity.

TL;DR + FAQ (read this first)

At-a-glance takeaways

• OA usage is role and org dependent, with stronger evidence for early-career and initial technical paths.
• Official guidance supports runnable code in a third-party coding tool during technical interviews.
• Supported tasks include strings, intervals, trees, graphs, caches, shortest paths, debugging, and complexity.
• Senior candidates may move faster toward loop or design, so confirm your schedule.
• Testing matters because Microsoft official guidance includes testing and engineering lifecycle signals.

Quick FAQ

Does every Microsoft SWE candidate get an OA?
No. The source marks OA usage as variable by candidate, org, and level.

Can I run code?
Official guidance says technical interviews use a third-party coding tool where code can run and compile.

What should I optimize for?
Correctness, tests, clean code, complexity, and explanation.

Is system design part of this stage?
Usually no. Design is more relevant in later loop stages, especially around L61+ and senior roles.

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1) How the assessment works

The online assessment or technical screen is an early coding filter. It may be automated or engineer-led, depending on the path. Official guidance for technical interviews says candidates use a third-party coding tool where code can run and compile, which changes how you should prepare: test your code instead of treating it as pseudocode.

Duration is not fixed in the official source. Treat the round as a timed coding exercise that expects a working solution and a clear explanation.

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2) Technical questions you may face

These examples reflect the source-supported question bank and official technical signals.

• Reverse the words in a string while preserving word order rules for spaces and punctuation.
• Merge a list of intervals. Then insert a new interval and keep the output merged.
• Validate whether a binary tree is a binary search tree. Now handle duplicate values according to a stated rule.
• Clone an undirected graph. Explain how your code avoids infinite loops.
• Implement an LRU cache with get and put. Then test update, eviction, and empty-cache behavior.
• Find the shortest path in a graph, then explain which algorithm you chose and why.
• Debug a failing unit test, identify the broken assumption, and update the code.
• After coding, analyze time and space complexity and run at least two edge cases.

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3) What strong performance looks like

Strong candidates use the tool well: they clarify, code, run or reason through examples, fix issues, and explain complexity. They also show testing discipline, which Microsoft official guidance names as part of technical evaluation.

Do not treat the runnable environment as permission to guess. Use it to validate a clear algorithm.

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4) Common failure modes

Not testing code even when the tool supports it. Testing is part of the official signal.

Stopping at a happy path. Edge cases and failed tests expose weak reasoning.

Ignoring complexity. Explain time and space cost before moving on.

Assuming OA applies to every senior path. Confirm your exact process.

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5) How to prepare

• Practice strings, intervals, trees, graphs, caches, shortest paths, and debugging.
• Run sample tests whenever the tool allows it.
• Write edge cases before final submission.
• Explain complexity and tradeoffs out loud.
• Ask the recruiter whether your screen is automated, engineer-led, or skipped.

The best preparation treats this as engineering, not just solving: code, test, revise, and explain.

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