As a Software Engineer at Reply, you sit at the intersection of high-level strategic consulting and deep-tech implementation. Unlike traditional product-focused roles, you will contribute to a vast network of specialized companies, meaning your work could range from developing IoT architectures for automotive giants to deploying cloud-native AI solutions for banking or public administration. You are not just writing code; you are building the digital backbone for global industrial groups. The role demands a balance of technical agility and business acumen. Because Reply operates as a network, you will often collaborate across different business units, requiring you to communicate complex technical concepts to non-technical stakeholders. Whether you are working on a greenfield project or optimizing an existing system, your contributions directly impact how Reply’s clients navigate the paradigms of cloud computing, digital media, and Industry 4.0. ##### Tip The Reply network is highly decentralized. While there is a central recruiting process, you will often be evaluated by the specific business unit (BU) that matches your profile and interests. Be prepared to research the specific company within the group that you are interviewing with.
Initial Screening Call
reportedA call with a recruiter to establish your profile and career interests.
What to demonstrate
- A call with a recruiter to establish your profile and career interests
- Depth in Programming Language Fundamentals
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.
Technical Interview
reportedIncludes a live coding session, discussion on previous projects, or a take-home task.
What to demonstrate
- Includes a live coding session, discussion on previous projects, or a take-home task
- Depth in Programming Language Fundamentals
How to prepare
- Answer aloud and timed: What are the principles of SOLID design, and can you provide an example of how you have applied them?
- Answer aloud and timed: How do you approach debugging a complex issue in a production environment?
2 candidate reports. Individual accounts describe a particular role and hiring cycle.
Reply Software Engineer English-language onsite interview experience
The process began with an HR phone call and continued with a video call. After that, I was invited on site for a technical interview and a more personal conversation. All communication and interviews were in English. The sequence was simple and orderly. I did not receive an offer, but I came away with a clear sense of the format and what later stages would involve. Location: Brüssel. Overall feed…
Read full experienceReply Software Engineer Interview Experience: React, Python, and LLM integration
I applied online and later had a technical interview for a full-stack role. The position centered on React and Python, with AI work and LLM integration. The discussion was clearly aimed at understanding how I would work with modern components and model-related use cases. I felt reasonably aligned with the topics, but I did not get an offer. My final impression was that the interview stayed tied t…
Read full experiencePracHub editorial advice for the preparation topics above.
Show your work
If you have a GitHub profile or have worked on interesting academic projects, be ready to explain the architecture and the decisions you made.
Prepare your "Why
The most successful candidates are those who can clearly articulate why they want to work in a consulting-style environment.
Be honest about your skills
If you don't know a specific technology, focus on your ability to learn it quickly rather than bluffing.
Research the group
Reply is a network of many companies. Knowing which specific company you are interviewing with will set you apart from other candidates.
Choose a category, try a prompt, then open its approach, worked solution or follow-up when you need it.
How would you handle memory management in your preferred language?
How would you handle memory management in your preferred language?
Approach
- Say what the runtime actually does before reasoning about the code.
- Name what is shared across threads and what owns each piece of state.
- Identify the window where an invariant is briefly untrue.
- 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?
Diff a projection against the primary without per-row point reads
The listing projection has drifted and some rows show a stale version. The primary holds 40,000,000 resource rows across 12,000 tenants while serving 1,200 writes and 14,000 reads per second. The obvious repair, reading each resource row and comparing its version against the projection, is correct and would eventually finish. Explain precisely why it is unacceptable here, then give a diff that finds the differing rows, state its complexity, and make it safe to run against a live primary. Replication lag is usually under 100 ms and is not bounded.
Approach
- Quantify the naive cost rather than calling it slow: 40,000,000 point reads at even 0.5 ms each is over five hours serialised, and the only lever is concurrency, which is exactly what you cannot spend. The primary's pool is sized for the write path, and 40,000,000 random reads evict the buffer cache that sustains the 85 percent cache hit rate, so the audit degrades the system it is auditing.
- Replace random access with one ordered pass per side. Both sides can be read in (tenant_id, resource_id) order, which is a sequential scan on each and a merge join in O(n) time and O(1) memory. For a dense diff that is the whole answer, and it reads the primary once instead of 40,000,000 times.
- For the expected sparse case, compare range hashes instead of rows: partition the key space, compute per range an order-independent aggregate over hash(resource_id, version), compare aggregates, and descend only into ranges that differ. With d differing rows and branching factor B, at most d ranges mismatch per level, so the drill-down examines O(d log_B(n/d)) ranges and reads full rows only in mismatching leaves.
- Aggregate with a sum modulo 2^64 or a multiset hash, never XOR. XOR is order-independent but self-cancelling, so two rows wrong in the same way, or a row duplicated on one side, leave the range aggregate matching and the range is declared clean.
Follow-up
- The diff reports 900 stale rows. How do you decide between patching those rows and rebuilding the projection from resource_revision?
- Same job, but the projection lives in a search index that cannot be scanned in key order. What changes?
Canonicalise a request body into a stable idempotency fingerprint
idempotency_key.request_fingerprint is a SHA-256 over the method, path and canonicalised body, and a retry whose fingerprint differs must be rejected with 422 rather than served the stored response. Write the canonicaliser. Bodies are JSON up to 256 KB nested at most 32 levels; clients vary key order, whitespace and unicode escaping, and some send 64-bit ids as JSON numbers. Produce a deterministic byte string such that semantically identical bodies match and any semantic difference does not. State your complexity and name two normalisations you refuse to perform.
Approach
- Parse once into a tree, then re-serialise under fixed rules: object keys sorted, array order preserved, one escaping convention, no insignificant whitespace. Parsing is O(n) and sorting keys is O(k log k) per object, so O(n log n) overall with O(depth) stack, and the 32-level cap is enforced during parsing because hostile nesting is how a canonicaliser becomes a stack overflow.
- Sort keys by their UTF-8 bytes and say why the obvious implementation is wrong in some runtimes: a default string comparison that orders by UTF-16 code units places surrogate pairs, meaning code points from U+10000 up, below U+E000 to U+FFFF, which is not UTF-8 byte order, so two services written in different languages disagree on the same document.
- Do not re-encode numbers through a double. IEEE-754 binary64 represents integers exactly only up to 2^53, so normalising a 19-digit id through a float changes it, and 1 against 1.0 cannot be reconciled without deciding whether they are the same value. Preserve the literal token, and require ids as strings at the API boundary if you want them comparable.
- Reject duplicate keys rather than picking one. JSON permits them and parsers disagree, most keeping the last, so any choice you make ties the fingerprint to a parser detail that the code handling the request does not necessarily share.
Follow-up
- A client sends the same logical request with an extra field your API ignores. Same key, different fingerprint, so you return 422. Is that the right answer?
- Where does the fingerprint get computed relative to request decompression and the body-size limit?
Keep soft-deleted accounts from blocking re-registration
app_user holds user_id, tenant_id, email CITEXT, password_hash (NULL for SSO principals), email_verified_at, auth_version, status ('invited','active','suspended','deactivated'), created_at, updated_at, deleted_at. Two live accounts for one address inside a tenant must be impossible, but an address freed by a soft delete must be reusable, and the same tenant may delete and re-register it repeatedly. Write the uniqueness DDL for PostgreSQL 16, then the equivalent for MySQL 8 where partial indexes do not exist, and say what each permits once three deleted rows already hold that address.
Approach
- Start from what is actually unique: not (tenant_id, email), but (tenant_id, email) among live rows. PostgreSQL says that directly — CREATE UNIQUE INDEX app_user_live_email ON app_user (tenant_id, email) WHERE deleted_at IS NULL. A full constraint over the same two columns burns the address permanently the first time someone deletes an account.
- Keep case-insensitivity in the type or the index, never in the application: CITEXT as given, or UNIQUE (tenant_id, lower(email)) as an expression index where the extension is unavailable. A case-sensitive unique column is exactly how two accounts for one human appear.
- For MySQL 8 the predicate has to move inside the key: add a discriminator column that is a constant 0 while the row is live and is set to user_id on delete, with UNIQUE (tenant_id, email, deleted_marker). Live rows share the constant and still collide; deleted rows differ from each other and stop colliding.
- State the NULL variant and its dependency: leaving the marker NULL for deleted rows also works, because a unique index treats NULLs as distinct — true in MySQL, and true in PostgreSQL only under the default NULLS DISTINCT, which PostgreSQL 15 lets you reverse. Check the polarity against the three existing deleted rows: constant-on-live is what preserves the collision you want, and reversing it silently admits duplicate live accounts.
Follow-up
- A deleted account re-registers with the same address the next day. Do the old resource rows follow the new user_id, and how does the API keep the two principals apart?
- How do you honour an erasure request while resource_revision.actor_user_id still references this table?
Hold a per-tenant active cap against concurrent creates
A tenant on the standard plan may hold at most 50 resources with status='active'. The create handler runs SELECT count(*) FROM resource WHERE tenant_id = $1 AND status = 'active', compares to 50, then inserts. Two creates arrive 3 ms apart on different instances and the tenant lands at 51. Name the anomaly, say whether PostgreSQL 16 READ COMMITTED or REPEATABLE READ prevents it and why, then give an implementation that holds the cap at READ COMMITTED with the exact statements. Finally, say what changes when the cap is 'at most one running export per tenant' on job_run.
Approach
- Name it: write skew. The two transactions read an overlapping set and write disjoint rows, so there is no row-level conflict for the engine to detect and each commit is individually legal.
- Rule out the levels precisely. READ COMMITTED takes a fresh snapshot per statement and takes no lock on the counted rows, so both see 49. PostgreSQL's REPEATABLE READ is snapshot isolation: it removes non-repeatable reads and phantoms within the snapshot but still admits write skew, because the anomaly is not a re-read of a changed row, it is a read of a set that a concurrent transaction invalidates. Only SERIALIZABLE closes it, by tracking the read dependency and aborting one transaction with SQLSTATE 40001 — a guarantee that exists only if the application re-runs the whole transaction from the read.
- Convert the set predicate into a single-row conflict: keep tenant.active_resource_count and run UPDATE tenant SET active_resource_count = active_resource_count + 1 WHERE tenant_id = $1 AND active_resource_count < 50 in the same transaction as the INSERT. Zero affected rows is the cap, returned as 409. The row lock serialises the decision at any isolation level, and contention is bounded to one tenant's row — which is also the fair-scheduling unit, unlike a global counter that would convoy every tenant behind one row.
- State the cost you just took on: a counter is a second source of truth that can drift, so every path that changes status must adjust it inside the same transaction, and a periodic reconciliation has to exist, with resource_revision as the authority for what the count should have been.
Follow-up
- A resource moves from archived back to active. Which statements change, and what breaks if the counter update and the status change land in different transactions?
- The cap becomes plan-dependent and a plan can change mid-month. Where does the number 50 live, and who reads it?
Can you explain the difference between OOP and functional programming paradigms?
Can you explain the difference between OOP and functional programming paradigms?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
What are the principles of SOLID design, and can you provide an example of how you have applied them?
What are the principles of SOLID design, and can you provide an example of how you have applied them?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
Can you explain how you would structure a simple API?
Can you explain how you would structure a simple API?
Approach
- Say who the caller is and what they do when the call fails halfway.
- Define the identity of a request so a retry cannot double-apply it.
- Separate accepted, pending, failed and confirmed; they are different facts.
- Design the error taxonomy before the success shape; callers branch on it.
Follow-up
- What happens if the caller retries after a timeout?
- How does a client discover it is on an old version of this contract?
Can you walk me through your thesis project and the technical challenges you faced?
Can you walk me through your thesis project and the technical challenges you faced?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
Which university courses did you find most relevant to this role, and why?
Which university courses did you find most relevant to this role, and why?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- 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 did you approach the choice of technologies for your personal or academic projects?
How did you approach the choice of technologies for your personal or academic projects?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
What were the most significant difficulties you encountered during your group projects?
What were the most significant difficulties you encountered during your group projects?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- 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 approach debugging a complex issue in a production environment?
How do you approach debugging a complex issue in a production environment?
Approach
- Establish what changed and when, before forming any theory.
- Pick a bisection that eliminates candidates whichever way it turns out.
- Check the instrumentation before believing the symptom.
- 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?
Built from the rounds and topics Reply candidates report.
Prepare, practise & reflect
One practical outcome each day. Spend longer where you need it.
0 / 7 done01Map the Reply loop
- Write out the reported sequence: Initial Screening Call, Technical Interview.
- 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 2 reported rounds, with the weakest marked.
02Work Programming Language Fundamentals
- Spend the session on Programming Language Fundamentals, which Reply candidates report being tested on.
- Write one worked example in Programming Language Fundamentals and time yourself on it.
Deliverable: One timed worked example in Programming Language Fundamentals.
03Work Data Structures
- Spend the session on Data Structures, which Reply candidates report being tested on.
- Write one worked example in Data Structures and time yourself on it.
Deliverable: One timed worked example in Data Structures.
04Work File/Text Processing
- Spend the session on File/Text Processing, which Reply candidates report being tested on.
- Write one worked example in File/Text Processing and time yourself on it.
Deliverable: One timed worked example in File/Text Processing.
05Answer out loud: Technical Foundations
- Answer aloud, timed: Can you explain the difference between OOP and functional programming paradigms?
- Answer aloud, timed: How would you handle memory management in your preferred language?
Deliverable: Spoken answers to 2 reported Technical Foundations question(s), under time.
06Answer out loud: Behavioral and Soft Skills
- Answer aloud, timed: Tell me about a project you worked on that you are particularly proud of.
- Answer aloud, timed: How do you handle situations where requirements are ambiguous or change frequently?
Deliverable: Spoken answers to 2 reported Behavioral and Soft Skills question(s), under time.
07Answer out loud: Academic and Project Experience
- Answer aloud, timed: Can you walk me through your thesis project and the technical challenges you faced?
- Answer aloud, timed: Which university courses did you find most relevant to this role, and why?
Deliverable: Spoken answers to 2 reported Academic and Project Experience question(s), under time.
Expand any day for tasks and deliverables. Your progress is saved on this device.
Behavioural rounds judge the decision you made and what it cost.
Tell me about a project you worked on that you are particularly proud of.
Tell me about a project you worked on that you are particularly proud of.
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- 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 situations where requirements are ambiguous or change frequently?
How do you handle situations where requirements are ambiguous or change frequently?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- 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?
Why do you want to work for Reply specifically, rather than a traditional product company?
Why do you want to work for Reply specifically, rather than a traditional product company?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- 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 manage your time when balancing multiple technical tasks?
How do you manage your time when balancing multiple technical tasks?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- 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?
What is your approach to learning new technologies or frameworks you have never used before?
What is your approach to learning new technologies or frameworks you have never used before?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- 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?
- 01
Tell me about a project you worked on that you are particularly proud of.
- 02
How do you handle situations where requirements are ambiguous or change frequently?
- 03
Why do you want to work for Reply specifically, rather than a traditional product company?
- 04
How do you manage your time when balancing multiple technical tasks?
How difficult is the technical interview?
It is generally considered manageable. The focus is on your ability to reason through problems rather than memorizing complex algorithms.
Reply Software Engineer candidate reports ↗How long does the process take?
It can vary, but once you are in the system, the process is often quite fast. Some candidates receive offers within a week of their final technical round.
Reply Software Engineer candidate reports ↗Is there a specific dress code?
While the culture is professional, it is also modern and tech-forward. Business casual is the standard expectation for interviews.
Reply Software Engineer candidate reports ↗Can I work remotely?
Reply has a flexible approach, but it often depends on the specific project and client requirements. Discuss this during your initial HR screening.
Reply Software Engineer candidate reports ↗What topics does Reply test in interviews?
Reply interviews most often cover Python, SQL, Problem Solving, Programming Languages (General), and Communication. The exact emphasis depends on the specific role you apply for.
Reply Software Engineer candidate reports ↗Sources & methodology 3 sources ↗
No official company page is cited. Rounds and questions come from candidate reports and PracHub editorial material; each source shows the date it was read.
- 01Reply Software Engineer candidate reports ↗
Company-reported rounds, questions and FAQ.
Candidate reports · Accessed 2026-09-22 - 02PracHub Software Engineer practice ↗
PracHub practice material, not company-reported.
PracHub page · Accessed 2026-09-22 - 03PracHub preparation framework ↗
PracHub preparation guidance.
PracHub page · Accessed 2026-09-22
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