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Known Software Engineer Interview Guide

Known Software Engineer interview guide: reported rounds, questions and how candidates describe the process.

The 60-second brief

A Software Engineer at Known plays a critical role in bridging the gap between advanced data science, modern media strategies, and highly scalable technology products. As a engineered-product driven agency, Known relies on its engineering team to build proprietary software that optimizes advertising campaigns, manages massive datasets, and delivers real-time analytics. Whether you are developing highly responsive user interfaces or architecting robust backend pipelines, your work directly impacts how some of the world's largest brands interact with their audiences. In this role, you will contribute to core products that handle complex data processing, automated media buying, and machine learning integrations.

This guide is scoped to a Software Engineer candidate at Known.

Focus areas

  • React (Product Engineer)
  • Software Engineering (Core Role)
  • Front-End Engineering

The Known interview process

Known candidates report 3 rounds over 3-5 weeks. The stages below are what candidates describe, not a published process.

Recruiter Call

Initial call to align on your background, career goals, and compensation expectations.

What to demonstrate

  • Initial call to align on your background, career goals, and compensation expectations
  • Depth in React (Product Engineer)

How to prepare

  • Be able to walk your CV end to end in two minutes, and say why this company specifically.
  • Have your salary expectations, notice period and location constraints ready, and ask for the rest of the loop in writing.

Tech Lead Meeting

30-minute meeting to discuss past experiences, technical preferences, and team requirements.

What to demonstrate

  • 30-minute meeting to discuss past experiences, technical preferences, and team requirements
  • Depth in React (Product Engineer)

How to prepare

  • Answer aloud and timed: Describe the lifecycle of a component and how you would implement custom hooks to reuse stateful logic.
  • Answer aloud and timed: How would you approach building a reusable component library that supports both accessibility and strict design system guidelines?

Technical Deep Dive

90-minute practical session focusing on real-world engineering scenarios, including coding and problem-solving.

What to demonstrate

  • 90-minute practical session focusing on real-world engineering scenarios
  • Including coding and problem-solving

How to prepare

  • Answer aloud and timed: Walk me through how you would handle asynchronous data fetching and error boundaries in a modern single-page application.
  • Answer aloud and timed: Implement a function to parse and validate complex configuration files, and explain how you would handle syntax or structural errors.

Where candidates lose points

Manage your time actively during the deep dive

The 90-minute technical deep dive is comprehensive. Keep track of the time and ensure you do not get stuck on a single optimization. It is better to have a fully working solution with minor configuration needs than an incomplete algorithm.

Verify your environment beforehand

Ensure your local development environment, IDE, and build tools are fully updated and functional before the technical interview. Having a smooth setup prevents unnecessary stress and technical delays during live coding.

Communicate your design trade-offs

Whenever you make a technical decision, explain why you chose that approach. Discussing the pros and cons of your chosen architecture or state management strategy shows maturity and depth as an engineer.

Questions & practice

Walk me through how you would handle asynchronous data fetching and error boundaries in a modern single-page a

Medium · React & Frontend Engineering

Walk me through how you would handle asynchronous data fetching and error boundaries in a modern single-page application.

Approach

  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

Implement a function to parse and validate complex configuration files, and explain how you would handle synta

Medium · Practical Coding & Environment Configura

Implement a function to parse and validate complex configuration files, and explain how you would handle syntax or structural errors.

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

Write a clean, optimized algorithm to solve a data manipulation problem, ensuring your solution handles edge c

Medium · Practical Coding & Environment Configura

Write a clean, optimized algorithm to solve a data manipulation problem, ensuring your solution handles edge cases and scale.

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

How do you configure and manage environment-specific settings files (such as Webpack, Babel, or application-le

Medium · Practical Coding & Environment Configura

How do you configure and manage environment-specific settings files (such as Webpack, Babel, or application-level configurations) to ensure smooth deployment pipelines?

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

How do you approach database schema design when building a system that requires both rapid transactional write

Medium · System Design & Architecture

How do you approach database schema design when building a system that requires both rapid transactional writes and complex analytical reads?

Approach

  1. Name the grain you start from and join outward from it.
  2. Check whether any join is one-to-many before aggregating, or the sums inflate.
  3. Say which index the query would use, and what makes it unusable.
  4. Handle the rows that do not match: that is usually the actual question.

Follow-up

  • How does the query change if that join becomes one-to-many?
  • What happens to this when the table is ten times larger?

Find version gaps and relay lag with window functions

Medium · window functions · event tables · frame semantics

outbox_event holds event_id, aggregate_type, aggregate_id, aggregate_version, event_type, payload, status ('pending','published','dead'), attempts, created_at, published_at. A projection is missing rows and you must decide whether the relay skipped events or the consumer dropped them. Write three queries over the last seven days: one listing every aggregate_id whose published aggregate_version sequence has a hole, one giving per-day counts with a running total, and one returning the newest published event per aggregate. For each, say where the window function is evaluated relative to WHERE and LIMIT. PostgreSQL 16.

Approach

  1. Gaps: compute lead(aggregate_version) OVER (PARTITION BY aggregate_id ORDER BY aggregate_version) in a subquery, then filter next_version <> aggregate_version + 1 in the outer query. Window functions are evaluated after WHERE, GROUP BY and HAVING and before the outer ORDER BY and LIMIT, so the predicate cannot sit in the same WHERE clause and PostgreSQL 16 has no QUALIFY.
  2. Say what the seven-day filter does to the answer: it truncates every partition, so the first row per aggregate has no predecessor inside the window and a hole spanning the boundary is invisible. Widen the window, or join to resource.version as the authority for the true maximum.
  3. Running total: SELECT date_trunc('day', created_at) AS d, count() AS n, sum(count()) OVER (ORDER BY date_trunc('day', created_at) ROWS UNBOUNDED PRECEDING). An aggregate inside a window call is legal because grouping runs before windowing. The grouping key is unique per row here so ROWS and RANGE agree, but write the frame anyway — over ungrouped rows with tied timestamps the default RANGE frame pulls in every peer row and the total jumps.
  4. Newest per aggregate: DISTINCT ON (aggregate_id) ... ORDER BY aggregate_id, aggregate_version DESC is the cheap PostgreSQL-only form when an index matches that order; row_number() OVER (PARTITION BY aggregate_id ORDER BY aggregate_version DESC) = 1 is the portable form and needs a subquery for the same evaluation-order reason as the gap query.

Follow-up

  • Relay failover redelivers events. Does a duplicate break the gap query, and how would you detect one from this table alone?
  • Turn the gap check into a continuous monitor rather than a query someone runs after an incident. What does it watch?

Explain how you manage complex state across a large-scale React application.

Medium · React & Frontend Engineering

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

How do you optimize a React application that is experiencing rendering bottlenecks when handling real-time dat

Medium · React & Frontend Engineering

How do you optimize a React application that is experiencing rendering bottlenecks when handling real-time data streams?

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

Describe the lifecycle of a component and how you would implement custom hooks to reuse stateful logic.

Medium · React & Frontend Engineering

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

How would you approach building a reusable component library that supports both accessibility and strict desig

Medium · React & Frontend Engineering

How would you approach building a reusable component library that supports both accessibility and strict design system guidelines?

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

Design a real-time analytics dashboard that needs to process and display millions of ad-impression events per

Medium · System Design & Architecture

Design a real-time analytics dashboard that needs to process and display millions of ad-impression events per minute.

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

How would you architect a backend service to support a new marketing automation feature, ensuring high availab

Medium · System Design & Architecture

How would you architect a backend service to support a new marketing automation feature, ensuring high availability and fault tolerance?

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

Explain how you would design a secure, versioned API that is consumed by both internal product teams and exter

Medium · System Design & Architecture

Explain how you would design a secure, versioned API that is consumed by both internal product teams and external clients.

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

Describe your process for debugging a memory leak in a running node service or client-side application.

Medium · Practical Coding & Environment Configura

Approach

  1. Establish what changed and when, before forming any theory.
  2. Pick a bisection that eliminates candidates whichever way it turns out.
  3. Check the instrumentation before believing the symptom.
  4. Separate the trigger from the cause; the deploy is rarely the bug.

Follow-up

  • What would you look at first, and what would it rule out?
  • How would you tell a cause from a coincidence here?

Suggested practice checklist

Built from the rounds and topics Known candidates report.

Day 1 — Map the Known loop

  • Write out the reported sequence: Recruiter Call, Tech Lead Meeting, Technical Deep Dive.
  • For each round, write one sentence on what it is judging, from the description above, and mark the one you are least ready for.

Deliverable: A one-page map of the 3 reported rounds, with the weakest marked.

Day 2 — Work React (Product Engineer)

  • Spend the session on React (Product Engineer), which Known candidates report being tested on.
  • Write one worked example in React (Product Engineer) and time yourself on it.

Deliverable: One timed worked example in React (Product Engineer).

Day 3 — Work Software Engineering (Core Role)

  • Spend the session on Software Engineering (Core Role), which Known candidates report being tested on.
  • Write one worked example in Software Engineering (Core Role) and time yourself on it.

Deliverable: One timed worked example in Software Engineering (Core Role).

Day 4 — Work Front-End Engineering

  • Spend the session on Front-End Engineering, which Known candidates report being tested on.
  • Write one worked example in Front-End Engineering and time yourself on it.

Deliverable: One timed worked example in Front-End Engineering.

Day 5 — Answer out loud: React & Frontend Engineering

  • Answer aloud, timed: Explain how you manage complex state across a large-scale React application.
  • Answer aloud, timed: How do you optimize a React application that is experiencing rendering bottlenecks when handling real-time data streams?

Deliverable: Spoken answers to 2 reported React & Frontend Engineering question(s), under time.

Day 6 — Answer out loud: Practical Coding & Environment Configuration

  • Answer aloud, timed: Implement a function to parse and validate complex configuration files, and explain how you would handle syntax or structural errors.
  • Answer aloud, timed: Write a clean, optimized algorithm to solve a data manipulation problem, ensuring your solution handles edge cases and scale.

Deliverable: Spoken answers to 2 reported Practical Coding & Environment Configuration question(s), under time.

Day 7 — Answer out loud: System Design & Architecture

  • Answer aloud, timed: Design a real-time analytics dashboard that needs to process and display millions of ad-impression events per minute.
  • Answer aloud, timed: How would you architect a backend service to support a new marketing automation feature, ensuring high availability and fault tolerance?

Deliverable: Spoken answers to 2 reported System Design & Architecture question(s), under time.

Behavioural preparation

Behavioural rounds judge the decision you made and what it cost.

Describe a time when you had to resolve a technical disagreement with a product manager or fellow engineer. Wh

Medium · Behavioral & Collaboration

Describe a time when you had to resolve a technical disagreement with a product manager or fellow engineer. What was the outcome?

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

How do you prioritize technical debt when working under tight deadlines to deliver a new product feature?

Medium · Behavioral & Collaboration

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

Tell me about a complex technical problem you solved recently. How did you explain your approach to non-techni

Medium · Behavioral & Collaboration

Tell me about a complex technical problem you solved recently. How did you explain your approach to non-technical stakeholders?

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

How do you handle a situation where you realize a deployed feature has introduced a critical bug in production

Medium · Behavioral & Collaboration

How do you handle a situation where you realize a deployed feature has introduced a critical bug in production?

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?