As a Software Engineer at Jellyfish, you play a pivotal role in developing sophisticated solutions that enhance our products and services. This position is critical to ensuring our technology scales efficiently, meets user needs, and drives business success. You will work closely with cross-functional teams to tackle complex challenges and contribute to projects that impact users worldwide. Your work will involve developing APIs, optimizing data handling, and implementing robust software solutions that cater to our clients' diverse requirements. The dynamic nature of this role provides opportunities for innovation and strategic influence, making it an exciting career choice for those passionate about software development and technology solutions. You'll contribute directly to products that help our clients achieve their goals, making your role both impactful and fulfilling.
Initial Screening
reportedThe first step involves assessing the candidate's basic qualifications and fit for the role.
What to demonstrate
- The first step involves assessing the candidate's basic qualifications and fit for the role
- Depth in Backend Engineering (APIs, Data, Scale)
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 Interviews
reportedMultiple interviews focusing on problem-solving skills and technical expertise.
What to demonstrate
- Multiple interviews focusing on problem-solving skills and technical expertise
- Depth in Backend Engineering (APIs, Data, Scale)
How to prepare
- Answer aloud and timed: Describe the difference between a relational database and a NoSQL database.
- Answer aloud and timed: How do you handle error management in your applications?
Final Round with Management
reportedA concluding interview with management to evaluate cultural fit and team dynamics.
What to demonstrate
- A concluding interview with management to evaluate cultural fit and team dynamics
- Depth in Backend Engineering (APIs, Data, Scale)
How to prepare
- Answer aloud and timed: Discuss your experience with cloud services and how you've utilized them in past projects.
- Answer aloud and timed: How would you approach debugging a performance issue in a production application?
PracHub editorial advice for the preparation topics above.
Demonstrate your passion
Show enthusiasm for technology and the work being done at Jellyfish. Candidates who convey genuine interest often stand out.
Prepare for behavioral questions
Think of specific examples from your past experiences that highlight your skills and contributions. Use the STAR method (Situation, Task, Action, Result) to structure your responses.
Familiarize yourself with company values
Understanding and aligning with Jellyfish's mission and culture can help you engage more effectively in interviews.
Practice coding problems
Regularly solve coding challenges to sharpen your skills. Platforms like LeetCode or HackerRank can be great resources for this.
Ask insightful questions
Prepare thoughtful questions to ask your interviewers about the team, projects, and company culture. This shows your engagement and helps you gauge fit.
Choose a category, try a prompt, then open its approach, worked solution or follow-up when you need it.
What are common pitfalls when working with asynchronous programming in JavaScript?
What are common pitfalls when working with asynchronous programming in JavaScript?
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?
Write a function to reverse a string in place.
Write a function to reverse a string in place.
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- 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 would you implement a binary search algorithm?
How would you implement a binary search algorithm?
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- 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?
Demonstrate how to traverse a binary tree using different traversal methods.
Demonstrate how to traverse a binary tree using different traversal methods.
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- 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?
Solve a problem involving sorting and searching algorithms.
Solve a problem involving sorting and searching algorithms.
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- 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?
Discuss the time and space complexity of your solutions.
Discuss the time and space complexity of your solutions.
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- 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?
Describe a database schema for a social media application.
Describe a database schema for a social media application.
Approach
- Name the grain you start from and join outward from it.
- Check whether any join is one-to-many before aggregating, or the sums inflate.
- Say which index the query would use, and what makes it unusable.
- 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?
Denormalise tenant onto revisions and backfill it live
resource_revision (revision_id, resource_id, version, actor_user_id, change_kind, patch, request_id, created_at) has 400M rows and no tenant column; tenant_id lives only on resource. Two reads need it: a tenant-scoped audit feed ordered by created_at DESC, and an offboarding purge. Both join back to resource today. Justify adding tenant_id to resource_revision against those two reads, name the anomaly the copy introduces and the constraint that prevents it, then give the ordered migration for a live table taking 1.2k writes/second — the lock each step takes, how the backfill is batched, and where each step stops being reversible. PostgreSQL 16.
Approach
- Justify from the access path rather than from taste. Without the column, the audit feed either scans resource_revision by created_at and discards other tenants' rows, or resolves the tenant's resource_ids first and probes with them — both proportional to the tenant's whole history rather than to one page. With (tenant_id, created_at DESC, revision_id DESC) it is a seek that stops at 50 rows, and the purge becomes a ranged delete instead of a join.
- Name the cost exactly: a second copy of a fact can disagree with the first. Make the disagreement unwritable rather than documented — add UNIQUE (resource_id, tenant_id) on resource so it can serve as a foreign-key target, then FOREIGN KEY (resource_id, tenant_id) REFERENCES resource (resource_id, tenant_id) on the revision table. A revision can then only ever carry its parent's tenant.
- Step one, expand: ALTER TABLE resource_revision ADD COLUMN tenant_id BIGINT NULL, with no default, so it is a catalogue change and no rewrite. It still needs ACCESS EXCLUSIVE for an instant, and that instant queues behind the longest open transaction on the table while every later query queues behind it — set lock_timeout to 2s and retry rather than wait.
- Step two, dual-write: deploy the writer that populates tenant_id on every new revision while reads still use the join. Reversible by redeploying the previous build, because nothing reads the column yet.
Follow-up
- The backfill is half finished and a rollback is required. What state is the table in, and what does the previous build do with a half-populated column?
- How do you verify the backfill actually finished, given rows are still being inserted while it runs?
Explain how you would optimize an API for performance.
Explain how you would optimize an API for performance.
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?
Describe the difference between a relational database and a NoSQL database.
Describe the difference between a relational database and a NoSQL database.
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?
Provide a solution for integrating a new feature into an existing system.
Provide a solution for integrating a new feature into an existing system.
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?
How do you prioritize tasks when working on multiple projects simultaneously?
How do you prioritize tasks when working on multiple projects simultaneously?
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?
Discuss a challenging bug you encountered and how you resolved it.
Discuss a challenging bug you encountered and how you resolved it.
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 would you design a scalable microservices architecture for an e-commerce application?
How would you design a scalable microservices architecture for an e-commerce application?
Approach
- Fix the scope first: who calls this, how often, and what they do when it fails.
- Name the read and write paths separately; they rarely have the same bottleneck.
- Choose a partition key and say what query it makes expensive.
- 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?
What considerations would you take into account when designing an API for third-party integrations?
What considerations would you take into account when designing an API for third-party integrations?
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?
How do you ensure system reliability and fault tolerance in your designs?
How do you ensure system reliability and fault tolerance in your designs?
Approach
- Fix the scope first: who calls this, how often, and what they do when it fails.
- Name the read and write paths separately; they rarely have the same bottleneck.
- Choose a partition key and say what query it makes expensive.
- 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?
Discuss the trade-offs between different architectural styles (e.g., monolithic vs. microservices).
Discuss the trade-offs between different architectural styles (e.g., monolithic vs. microservices).
Approach
- Fix the scope first: who calls this, how often, and what they do when it fails.
- Name the read and write paths separately; they rarely have the same bottleneck.
- Choose a partition key and say what query it makes expensive.
- 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 approach debugging a performance issue in a production application?
How would you approach debugging a performance issue in a production application?
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 Jellyfish candidates report.
Prepare, practise & reflect
One practical outcome each day. Spend longer where you need it.
0 / 7 done01Map the Jellyfish loop
- Write out the reported sequence: Initial Screening, Technical Interviews, Final Round with Management.
- 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.
02Work Backend Engineering (APIs, Data, Scale)
- Spend the session on Backend Engineering (APIs, Data, Scale), which Jellyfish candidates report being tested on.
- Write one worked example in Backend Engineering (APIs, Data, Scale) and time yourself on it.
Deliverable: One timed worked example in Backend Engineering (APIs, Data, Scale).
03Work API Development
- Spend the session on API Development, which Jellyfish candidates report being tested on.
- Write one worked example in API Development and time yourself on it.
Deliverable: One timed worked example in API Development.
04Work Coding Interviews (General)
- Spend the session on Coding Interviews (General), which Jellyfish candidates report being tested on.
- Write one worked example in Coding Interviews (General) and time yourself on it.
Deliverable: One timed worked example in Coding Interviews (General).
05Answer out loud: Technical / Domain Questions
- Answer aloud, timed: Explain how you would optimize an API for performance.
- Answer aloud, timed: What are common pitfalls when working with asynchronous programming in JavaScript?
Deliverable: Spoken answers to 2 reported Technical / Domain Questions question(s), under time.
06Answer out loud: Problem-Solving / Case Studies
- Answer aloud, timed: How would you approach debugging a performance issue in a production application?
- Answer aloud, timed: Describe a time when you had to make a critical decision under pressure.
Deliverable: Spoken answers to 2 reported Problem-Solving / Case Studies question(s), under time.
07Answer out loud: Behavioral / Leadership
- Answer aloud, timed: Describe a time when you had to work with a difficult teammate. How did you handle it?
- Answer aloud, timed: How do you ensure effective communication in a remote work environment?
Deliverable: Spoken answers to 2 reported Behavioral / Leadership 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.
How do you handle error management in your applications?
How do you handle error management in your applications?
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?
Discuss your experience with cloud services and how you've utilized them in past projects.
Discuss your experience with cloud services and how you've utilized them in past projects.
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?
Describe a time when you had to make a critical decision under pressure.
Describe a time when you had to make a critical decision under pressure.
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?
Describe a time when you had to work with a difficult teammate. How did you handle it?
Describe a time when you had to work with a difficult teammate. How did you handle it?
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 ensure effective communication in a remote work environment?
How do you ensure effective communication in a remote work environment?
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 mentoring junior engineers or new team members?
What is your approach to mentoring junior engineers or new team members?
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?
Tell me about a significant failure you experienced and what you learned from it.
Tell me about a significant failure you experienced and what you learned from it.
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 conflicts within a team?
How do you manage conflicts within a team?
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
How do you handle error management in your applications?
- 02
Discuss your experience with cloud services and how you've utilized them in past projects.
- 03
Describe a time when you had to make a critical decision under pressure.
- 04
Describe a time when you had to work with a difficult teammate. How did you handle it?
How difficult is the interview process at Jellyfish?
The interview process can vary in difficulty, but candidates should expect a mix of technical challenges and behavioral assessments. Preparation is key, and candidates typically find focused study on relevant topics beneficial.
Jellyfish Software Engineer candidate reports ↗What differentiates successful candidates?
Successful candidates often demonstrate a strong technical foundation, clear communication skills, and a genuine alignment with the company's values. Being able to articulate past experiences and problem-solving approaches is crucial.
Jellyfish Software Engineer candidate reports ↗What is the culture like at Jellyfish?
Jellyfish fosters a collaborative and innovative culture. Employees are encouraged to share ideas, support one another, and contribute to projects that make a meaningful impact.
Jellyfish Software Engineer candidate reports ↗What is the typical timeline from the initial screen to an offer?
The timeline can vary, but candidates generally can expect to hear back within a few weeks after their initial interview. The process may include multiple rounds of interviews, so patience and proactive follow-up are encouraged.
Jellyfish Software Engineer candidate reports ↗Are there remote work options?
Jellyfish offers flexible work arrangements, including remote opportunities, depending on the specific team and role. Candidates should inquire about the working environment during their interviews.
Jellyfish Software Engineer candidate reports ↗What topics does Jellyfish test in interviews?
Jellyfish interviews most often cover Stakeholder Communication, API Development, Problem Solving, Interview Process Management, and SQL. The exact emphasis depends on the specific role you apply for.
Jellyfish 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.
- 01Jellyfish 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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