As a Software Engineer at Cassini Technologies, you play a pivotal role in transforming the landscape of cataract surgery through innovative software solutions. Your work directly impacts surgeons' capabilities to perform intricate procedures with precision, thereby enhancing patient outcomes. By developing and refining advanced algorithms and software systems, you contribute to the creation of products that blend medical science with cutting-edge technology. This position is not just about coding; it involves taking ownership of entire features throughout the research and development lifecycle. You will be responsible for designing, implementing, and maintaining robust software that meets the stringent standards of the medical industry. The complexity of the systems you will work on, coupled with the autonomy you will enjoy, makes this role both challenging and rewarding. Expect to collaborate with cross-functional teams, ensuring that your contributions are both technically sound and aligned with the clinical needs of surgeons globally.
Initial Screening
reportedThe first step involves an initial screening to assess your qualifications and fit for the role.
What to demonstrate
- The first step involves an initial screening to assess your qualifications and fit for the role
- Depth in Python
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 Assessments
reportedCandidates will undergo technical assessments to evaluate their coding and problem-solving skills.
What to demonstrate
- Candidates will undergo technical assessments to evaluate their coding and problem-solving skills
- Depth in Python
How to prepare
- Answer aloud and timed: Describe your experience with SQLAlchemy and how it integrates with FastAPI.
- Answer aloud and timed: What strategies do you use for optimizing database performance?
Behavioral Interviews
reportedBehavioral interviews focus on your past experiences and how you align with the company's culture.
What to demonstrate
- Behavioral interviews focus on your past experiences and how you align with the company's culture
- Depth in Python
How to prepare
- Prepare three examples from your own work, each with a decision you made and an outcome you can quantify.
- Re-read the description of the behavioral interviews above and write down what you would ask to confirm before it.
System Design Discussions
reportedYou will participate in discussions centered around system design to demonstrate your architectural skills.
What to demonstrate
- You will participate in discussions centered around system design to demonstrate your architectural skills
- Depth in Python
How to prepare
- Answer aloud and timed: How would you architect a service that handles high volumes of data input from surgical instruments?
- Answer aloud and timed: Discuss the considerations for building a secure API in a medical environment.
Final Discussions
reportedThe final discussions involve conversations with team members to assess collaboration and communication skills.
What to demonstrate
- The final discussions involve conversations with team members to assess collaboration and communication skills
- Depth in Python
How to prepare
- Answer aloud and timed: What factors do you consider when deciding between microservices and a monolithic architecture?
- Answer aloud and timed: Explain how you would implement error handling in a distributed system.
PracHub editorial advice for the preparation topics above.
Practice coding under time constraints
Given the emphasis on coding skills, practicing timed coding challenges can help you become more comfortable under pressure.
Familiarize yourself with medical standards
Understanding the basics of medical regulations can provide context for your technical work and demonstrate your commitment to the domain.
Prepare for behavioral questions
Reflect on past experiences that showcase your problem-solving abilities and teamwork skills, as these are central to the company's values.
Engage with the company's mission
Be prepared to discuss why you are passionate about improving patient outcomes and how your work contributes to this goal.
Choose a category, try a prompt, then open its approach, worked solution or follow-up when you need it.
Write a function in Python to flatten a nested list.
Write a function in Python to flatten a nested list.
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?
Given a string, implement an algorithm to check if it is a palindrome.
Given a string, implement an algorithm to check if it is a palindrome.
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?
Can you explain the time complexity of your solution to a specific problem?
Can you explain the time complexity of your solution to a specific problem?
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 caching mechanism for a frequently accessed resource?
How would you implement a caching mechanism for a frequently accessed resource?
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?
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?
Explain why the owner filter ignores the listing index
The only index on resource is (tenant_id, status, updated_at DESC, resource_id DESC). A new endpoint returns one user's resources across all statuses, newest created first: WHERE tenant_id = $1 AND owner_user_id = $2 ORDER BY created_at DESC LIMIT 20. On a tenant with 2M rows it takes 900 ms and EXPLAIN shows a sort above a large scan. Explain precisely why the existing index cannot serve it, give the index that can, and state which of these the new index still will not help: owner_user_id alone across tenants; the same query ordered by updated_at. PostgreSQL 16.
Approach
- Separate the two jobs an index does. For filtering, a composite btree is seekable only on a left prefix, so with no predicate on status the scan can at best range over tenant_id and test owner_user_id per row; PostgreSQL 16 has no btree skip scan to jump the unconstrained column.
- For ordering, the index is sorted by (status, updated_at) within a tenant and not by created_at, so the LIMIT cannot stop early: every matching row is read and then sorted. That is the 'Sort Method: top-N heapsort' line, and it is why the plan reads 2M rows to answer with 20.
- Derive the replacement from the access path — equality, equality, then the ordering column: CREATE INDEX CONCURRENTLY ON resource (tenant_id, owner_user_id, created_at DESC). The scan seeks to the (tenant, owner) range and walks 20 entries in order, so the Sort node disappears along with the row-read.
- Treat INCLUDE (title, status) as conditional, not free. An index-only scan still visits the heap for any row whose page is not marked all-visible, so on a table taking 1.2k writes/second the win depends on autovacuum keeping the visibility map current, and the wider index costs more on every insert.
Follow-up
- 90% of rows are status='active'. Would a partial index WHERE status = 'active' change your answer, and for which of the three queries?
- A dashboard runs this for 40 owners in one page load. What changes about the design?
Explain the differences between FastAPI and Flask.
Explain the differences between FastAPI and Flask.
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 ensure the correctness of your code in a heavily type-annotated codebase?
How do you ensure the correctness of your code in a heavily type-annotated codebase?
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 strategies do you use for optimizing database performance?
What strategies do you use for optimizing database performance?
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 the role of Docker in modern software development workflows?
Can you explain the role of Docker in modern software development workflows?
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?
Design a system for a web application that allows surgeons to access patient data in real-time.
Design a system for a web application that allows surgeons to access patient data in real-time.
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 architect a service that handles high volumes of data input from surgical instruments?
How would you architect a service that handles high volumes of data input from surgical instruments?
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 considerations for building a secure API in a medical environment.
Discuss the considerations for building a secure API in a medical environment.
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?
What factors do you consider when deciding between microservices and a monolithic architecture?
What factors do you consider when deciding between microservices and a monolithic architecture?
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?
Explain how you would implement error handling in a distributed system.
Explain how you would implement error handling in a distributed system.
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?
Walk us through a challenging bug you encountered in a past project and how you resolved it.
Walk us through a challenging bug you encountered in a past project 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?
Describe a situation where you had to balance technical debt against new feature development.
Describe a situation where you had to balance technical debt against new feature development.
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 steps would you take to improve the performance of an existing application?
What steps would you take to improve the performance of an existing application?
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 prioritize tasks when working on multiple features simultaneously?
How do you prioritize tasks when working on multiple features 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?
How do you ensure effective communication in a distributed team?
How do you ensure effective communication in a distributed team?
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?
Write a function that fetches data from an API and processes the response.
Write a function that fetches data from an API and processes the response.
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 would you approach debugging a system that intermittently fails under load?
How would you approach debugging a system that intermittently fails under load?
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 Cassini Technologies candidates report.
Prepare, practise & reflect
One practical outcome each day. Spend longer where you need it.
0 / 7 done01Map the Cassini Technologies loop
- Write out the reported sequence: Initial Screening, Technical Assessments, Behavioral Interviews, System Design Discussions, Final Discussions.
- 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 5 reported rounds, with the weakest marked.
02Work Python
- Spend the session on Python, which Cassini Technologies candidates report being tested on.
- Write one worked example in Python and time yourself on it.
Deliverable: One timed worked example in Python.
03Work Type Annotations
- Spend the session on Type Annotations, which Cassini Technologies candidates report being tested on.
- Write one worked example in Type Annotations and time yourself on it.
Deliverable: One timed worked example in Type Annotations.
04Work TypeScript
- Spend the session on TypeScript, which Cassini Technologies candidates report being tested on.
- Write one worked example in TypeScript and time yourself on it.
Deliverable: One timed worked example in TypeScript.
05Answer out loud: Technical / Domain Questions
- Answer aloud, timed: Explain the differences between FastAPI and Flask.
- Answer aloud, timed: How do you ensure the correctness of your code in a heavily type-annotated codebase?
Deliverable: Spoken answers to 2 reported Technical / Domain Questions question(s), under time.
06Answer out loud: System Design / Architecture
- Answer aloud, timed: Design a system for a web application that allows surgeons to access patient data in real-time.
- Answer aloud, timed: How would you architect a service that handles high volumes of data input from surgical instruments?
Deliverable: Spoken answers to 2 reported System Design / Architecture question(s), under time.
07Answer out loud: Problem-Solving / Case Studies
- Answer aloud, timed: Walk us through a challenging bug you encountered in a past project and how you resolved it.
- Answer aloud, timed: How would you approach debugging a system that intermittently fails under load?
Deliverable: Spoken answers to 2 reported Problem-Solving / Case Studies 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.
Describe your experience with SQLAlchemy and how it integrates with FastAPI.
Describe your experience with SQLAlchemy and how it integrates with FastAPI.
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 team member. How did you handle it?
Describe a time when you had to work with a difficult team member. 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?
Can you give an example of a time you took initiative in a project?
Can you give an example of a time you took initiative in a project?
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 do you do to stay motivated when working remotely?
What do you do to stay motivated when working remotely?
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 feedback and criticism of your work?
How do you handle feedback and criticism of your work?
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
Describe your experience with SQLAlchemy and how it integrates with FastAPI.
- 02
Describe a time when you had to work with a difficult team member. How did you handle it?
- 03
Can you give an example of a time you took initiative in a project?
- 04
What do you do to stay motivated when working remotely?
What is the typical difficulty level of the interviews?
The interviews are designed to be challenging but fair, focusing on both technical skills and cultural fit. Candidates should prepare for in-depth technical assessments and behavioral discussions.
Cassini Technologies Software Engineer candidate reports ↗What differentiates successful candidates?
Successful candidates demonstrate not only strong technical abilities but also the capacity to communicate effectively and work autonomously in a remote environment. Showing a passion for the impact of your work in the medical field can also set you apart.
Cassini Technologies Software Engineer candidate reports ↗What is the culture like at Cassini Technologies?
The culture is collaborative, with an emphasis on autonomy and continuous improvement. Employees are encouraged to take ownership of their work while contributing to team goals.
Cassini Technologies Software Engineer candidate reports ↗What is the typical timeline from initial screen to offer?
The timeline can vary, but candidates usually receive feedback within a couple of weeks after each interview stage. The process aims to balance thoroughness with efficiency.
Cassini Technologies Software Engineer candidate reports ↗Are there specific remote work expectations?
Yes, while the role is fully remote, candidates should be comfortable with asynchronous communication and demonstrate effective collaboration with distributed teams.
Cassini Technologies Software Engineer candidate reports ↗What topics does Cassini Technologies test in interviews?
Cassini Technologies interviews most often cover Python, Type Annotations, TypeScript, React, and Mypy. The exact emphasis depends on the specific role you apply for.
Cassini Technologies 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.
- 01Cassini Technologies 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
Explore related engineering environments and compare the preparation focus.
Discord Software Engineer Interview Guide
Database practice for Discord candidates: how an index changes a query plan, and which anomalies survive a given isolation level, since read committed still permits non-repeatable reads.
Rystad Energy Software Engineer Interview Guide
Prepare for Rystad Energy software interviews with worked Python validation, OOP and decorator examples, plus an ingestion case and practical checks.
Steadily Software Engineer Interview Guide
What Steadily asks Software Engineer candidates, from reported rounds and questions.
Samsung Ads Software Engineer Interview Guide
What Samsung Ads asks Software Engineer candidates, from reported rounds and questions.