As a Software Engineer at Tonal, you will work at the intersection of physical hardware, complex firmware, and high-performance digital applications. Tonal is not just an app-driven platform; it is an entire connected fitness ecosystem powered by an intelligent, electromagnetic resistance engine. Engineers here are responsible for translating physical human movement into real-time digital data, creating a seamless, responsive, and deeply personalized workout experience. Your work will directly impact how the system controls its digital weights, tracks user biometrics, and delivers interactive, low-latency coaching content. Because Tonal integrates hardware and software so closely, your code will live on a device that physically interacts with users. This requires a heightened focus on safety, reliability, and real-time performance that goes far beyond standard web or mobile application development. Whether you are optimizing local device algorithms, designing robust APIs for cloud communication, or collaborating with hardware teams on sensor integration, your contributions will define the future of intelligent strength training. It is a challenging, highly cross-functional environment where software engineering directly shapes a physical product.
Recruiter Screen
reportedStandard discussion with a recruiter about your background.
What to demonstrate
- Standard discussion with a recruiter about your background
- Depth in Software Engineering (General)
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 Conversation
reportedTechnical discussion with a hiring manager or team lead.
What to demonstrate
- Technical discussion with a hiring manager or team lead
- Depth in Software Engineering (General)
How to prepare
- Answer aloud and timed: Optimize a resource-constrained algorithm to run efficiently on an embedded or local client device without exhausting memory.
- Answer aloud and timed: Design a data structure to store and rapidly query historical workout metrics on a localized device.
Take-Home Assignment
reportedComplete a domain-specific assignment that mimics real-world engineering challenges.
What to demonstrate
- Complete a domain-specific assignment that mimics real-world engineering challenges
- Depth in Software Engineering (General)
How to prepare
- Answer aloud and timed: Design an API layer that allows a physical fitness device to communicate state changes to a cloud backend with minimal latency.
- Answer aloud and timed: How would you architect a system to sync local workout data back to a central database when the device experiences intermittent internet connectivity?
Final Interview Stage
reportedMulti-round panel interview with team members and technical leaders, covering your assignment and problem-solving.
What to demonstrate
- Multi-round panel interview with team members and technical leaders
- Covering your assignment and problem-solving
How to prepare
- Answer aloud and timed: Walk us through your design for a take-home assignment, explaining how you structured your classes, managed data flow, and ensured thread safety.
- Answer aloud and timed: Describe how you would build a testing framework to simulate physical sensor inputs for automated software quality engineering (SQE) testing.
PracHub editorial advice for the preparation topics above.
Prepare for Cross-Functional Interviewers
You may find yourself interviewing with managers or engineers from different departments, such as mechanical engineering or product design. Tailor your communication style to your audience; avoid overly dense software jargon when speaking with non-software stakeholders, and focus on how your work enables theirs.
During technical assignment reviews, be ready for interviewers to challenge your design choices
They are testing your engineering maturity, receptiveness to feedback, and ability to defend your decisions constructively. Avoid becoming defensive; instead, treat the review as a collaborative brainstorming session with a peer.
Inquire About Hardware Constraints
Show your product awareness by asking questions about the physical constraints of the device. Inquire about memory limitations, CPU thermal throttling, or sensor latency. This demonstrates that you understand the unique challenges of writing software for a connected hardware product.
Be Proactive with HR
Because Tonal is a growing company, recruitment processes can sometimes feel hectic. Stay highly organized, keep track of your interviewers' names, and do not hesitate to reach out to your recruiter if you experience delays in scheduling or feedback.
Choose a category, try a prompt, then open its approach, worked solution or follow-up when you need it.
Implement an algorithm to process real-time sensor telemetry, filtering out noise from physical user movements
Implement an algorithm to process real-time sensor telemetry, filtering out noise from physical user movements.
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?
Write a clean, object-oriented solution to manage state transitions for a connected device undergoing various
Write a clean, object-oriented solution to manage state transitions for a connected device undergoing various operational modes.
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?
Optimize a resource-constrained algorithm to run efficiently on an embedded or local client device without exh
Optimize a resource-constrained algorithm to run efficiently on an embedded or local client device without exhausting memory.
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?
Walk us through your design for a take-home assignment, explaining how you structured your classes, managed da
Walk us through your design for a take-home assignment, explaining how you structured your classes, managed data flow, and ensured thread safety.
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?
Stop tag and share joins from fanning out a page
resource_tag is (resource_id, tag_id) with PK (resource_id, tag_id); resource_share is (resource_id, shared_with_user_id, permission). The tagged-and-shared listing inner-joins resource to both, filters tenant_id, tag_id = ANY($2) and shared_with_user_id = $3, orders by updated_at DESC and takes 50. Pages come back with fewer than 50 distinct resources and the total in the header is far too high. Explain the row multiplication, rewrite both the page query and the count query so each is correct, and name the index each one needs. PostgreSQL 16.
Approach
- Do the arithmetic against the predicates that are actually there. An inner join emits one row per matching child row, and both joins are filtered: tag_id = ANY($2) admits only the requested tags, shared_with_user_id = $3 admits one user's share rows. So a resource holding three of the requested tags and shared with $3 once yields three rows, not one — the multiplier is its count of matching tags times its share rows for that single user, and that second factor is 1 unless the table admits duplicate (resource_id, shared_with_user_id) pairs. LIMIT 50 then limits rows rather than resources, and COUNT(*) counts pairs — the header is the product, not the population.
- Reject DISTINCT as the fix. It deduplicates after the product has been built, so the planner must materialise and sort the fanned-out set before the LIMIT can apply, and it leaves any SUM or AVG in the same select list wrong.
- Rewrite both filters as semi-joins, keeping resource as the only row source: AND EXISTS (SELECT 1 FROM resource_tag rt WHERE rt.resource_id = r.resource_id AND rt.tag_id = ANY($2)) and the same shape against resource_share. A semi-join stops at the first match per resource and preserves the driving index order, so ORDER BY updated_at DESC, resource_id DESC LIMIT 50 still stops after 50 rows.
- Count with the same predicates and no join at all: SELECT count(*) FROM resource r WHERE r.tenant_id = $1 AND r.status = 'active' AND EXISTS (...) AND EXISTS (...). Nothing multiplies a resource, so the number is the population.
Follow-up
- The filter changes from 'any of these tags' to 'all of these tags'. Rewrite it and state what it costs relative to the ANY form.
- A resource can be shared with the same user twice under different permissions. Does your count change, and should it?
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?
Design a data structure to store and rapidly query historical workout metrics on a localized device.
Design a data structure to store and rapidly query historical workout metrics on a localized device.
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?
Design an API layer that allows a physical fitness device to communicate state changes to a cloud backend with
Design an API layer that allows a physical fitness device to communicate state changes to a cloud backend with minimal latency.
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?
Describe how you would build a testing framework to simulate physical sensor inputs for automated software qua
Describe how you would build a testing framework to simulate physical sensor inputs for automated software quality engineering (SQE) testing.
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 me through a highly complex technical project you led, focusing on the trade-offs you made during the arc
Walk me through a highly complex technical project you led, focusing on the trade-offs you made during the architectural phase.
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 system to sync local workout data back to a central database when the device experie
How would you architect a system to sync local workout data back to a central database when the device experiences intermittent internet connectivity?
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 Tonal candidates report.
Prepare, practise & reflect
One practical outcome each day. Spend longer where you need it.
0 / 7 done01Map the Tonal loop
- Write out the reported sequence: Recruiter Screen, Technical Conversation, Take-Home Assignment, Final Interview Stage.
- 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 4 reported rounds, with the weakest marked.
02Work Software Engineering (General)
- Spend the session on Software Engineering (General), which Tonal candidates report being tested on.
- Write one worked example in Software Engineering (General) and time yourself on it.
Deliverable: One timed worked example in Software Engineering (General).
03Work Technical Interviewing
- Spend the session on Technical Interviewing, which Tonal candidates report being tested on.
- Write one worked example in Technical Interviewing and time yourself on it.
Deliverable: One timed worked example in Technical Interviewing.
04Work Coding Practice / Algorithmic Coding
- Spend the session on Coding Practice / Algorithmic Coding, which Tonal candidates report being tested on.
- Write one worked example in Coding Practice / Algorithmic Coding and time yourself on it.
Deliverable: One timed worked example in Coding Practice / Algorithmic Coding.
05Answer out loud: Coding & Algorithmic Execution
- Answer aloud, timed: Implement an algorithm to process real-time sensor telemetry, filtering out noise from physical user movements.
- Answer aloud, timed: Write a clean, object-oriented solution to manage state transitions for a connected device undergoing various operational modes.
Deliverable: Spoken answers to 2 reported Coding & Algorithmic Execution question(s), under time.
06Answer out loud: System Architecture & Domain Design
- Answer aloud, timed: Design an API layer that allows a physical fitness device to communicate state changes to a cloud backend with minimal latency.
- Answer aloud, timed: How would you architect a system to sync local workout data back to a central database when the device experiences intermittent internet connectivity?
Deliverable: Spoken answers to 2 reported System Architecture & Domain Design question(s), under time.
07Answer out loud: Experience & Cross-Functional Collaboration
- Answer aloud, timed: Walk me through a highly complex technical project you led, focusing on the trade-offs you made during the architectural phase.
- Answer aloud, timed: Describe a time when you had to work with hardware engineers or test engineers (TE) to diagnose a software issue that only occurred on physical devices.
Deliverable: Spoken answers to 2 reported Experience & Cross-Functional Collaboration 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 a time when you had to work with hardware engineers or test engineers (TE) to diagnose a software iss
Describe a time when you had to work with hardware engineers or test engineers (TE) to diagnose a software issue that only occurred on physical devices.
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 product designers propose a feature that introduces significant technical d
How do you handle situations where product designers propose a feature that introduces significant technical debt or latency?
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?
Explain your experience working with external suppliers or research and development (RD) teams to integrate th
Explain your experience working with external suppliers or research and development (RD) teams to integrate third-party components into a software stack.
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 a time when you had to work with hardware engineers or test engineers (TE) to diagnose a software issue that only occurred on physical devices.
- 02
How do you handle situations where product designers propose a feature that introduces significant technical debt or latency?
- 03
Explain your experience working with external suppliers or research and development (RD) teams to integrate third-party components into a software stack.
How technical is the interview process for Software Engineers?
The process is highly technical and very specific to the role. You will be evaluated on your coding fluency, system design capabilities, and practical engineering skills. Be prepared for deep-dive questions about your past technical decisions and your take-home assignment.
Tonal Software Engineer candidate reports ↗Can I choose my preferred programming language for the coding rounds?
In some rounds, you may be required to code in the specific language used by the team you are interviewing with (such as Kotlin or C++). It is highly recommended to clarify language expectations with your recruiter early in the process and practice coding in Tonal's primary stack.
Tonal Software Engineer candidate reports ↗What is the company culture like for engineers?
Tonal operates with a fast-paced, collaborative startup energy. Engineers are highly passionate about fitness and technology, and there is a strong emphasis on cross-functional teamwork. Because the product is physical, you will regularly interact with hardware, design, and product quality teams.
Tonal Software Engineer candidate reports ↗How long does the hiring process typically take?
The process generally takes between three to six weeks from the initial recruiter screen to the final decision. However, scheduling logistics can sometimes vary, so maintaining open communication with your coordinator is key.
Tonal Software Engineer candidate reports ↗What topics does Tonal test in interviews?
Tonal interviews most often cover Project Management, Software Engineering (General), Model Deployment / Shipped Models, Program Management, and Technical Interviewing. The exact emphasis depends on the specific role you apply for.
Tonal 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.
- 01Tonal 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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