Jam City Software Engineer Interview Guide

The 60-second brief

As a Software Engineer at Jam City, you are at the heart of creating engaging mobile experiences that reach millions of players worldwide. This role is not just about writing code; it is about architecting the systems that power complex game mechanics, optimizing performance for diverse mobile hardware, and collaborating with cross-functional teams including designers, artists, and producers to bring creative visions to life. You will contribute to a fast-paced environment where your work directly impacts user retention and the overall success of flagship titles. Whether you are implementing game systems, optimizing data structures for high-traffic features, or solving complex 3D math problems, your technical contributions are the foundation of the Jam City player experience.

This guide is scoped to a Software Engineer candidate at Jam City.

Focus areas

• Unity
• C#
• Object-Oriented Programming (Classes/Structs)

The Jam City interview process

Jam City candidates report 5 rounds over 4-6 weeks. The stages below are what candidates describe, not a published process.

Automated Test

Candidates begin with an automated test to assess coding abilities.

What to demonstrate

• Candidates begin with an automated test to assess coding abilities
• Depth in Unity

How to prepare

• Answer aloud and timed: What is the difference between a class and a struct in C#?
• Answer aloud and timed: Can you explain the difference between pass-by-reference and pass-by-value?

Live Technical Interviews

Multiple rounds of live technical interviews conducted by senior developers.

What to demonstrate

• Multiple rounds of live technical interviews conducted by senior developers
• Depth in Unity

How to prepare

• Answer aloud and timed: What are the main differences between static and readonly keywords?
• Answer aloud and timed: How do you utilize Unity Coroutines, and what are their common pitfalls?

Problem-Solving Assessment

Interviewers gauge candidates' problem-solving methodologies in real-time.

What to demonstrate

• Interviewers gauge candidates' problem-solving methodologies in real-time
• Depth in Unity

How to prepare

• Answer aloud and timed: What is the role of the camera in game development?
• Answer aloud and timed: How would you implement a game chest or reward system? What data structures would you select?

Team Interaction

Candidates interact with various team members, including engineers and designers.

What to demonstrate

• Candidates interact with various team members
• Including engineers and designers

How to prepare

• Answer aloud and timed: How do you handle game or player data storage using JSON?
• Answer aloud and timed: Can you describe how to implement a match-3 mechanic or grid-based game logic?

Cultural Fit Evaluation

Assessment of how candidates align with the studio's collaborative environment.

What to demonstrate

• Assessment of how candidates align with the studio's collaborative environment
• Depth in Unity

How to prepare

• Answer aloud and timed: How would you implement a visual effect, such as an earthquake, within the game engine?
• Answer aloud and timed: What design patterns (e.g., Singleton) do you find most useful in game architecture?

Where candidates lose points

Prioritize Communication

When coding, speak your thoughts aloud. Interviewers are more interested in your problem-solving path than the final code snippet.

Be Honest About Experience

If you are newer to game development, emphasize your strong general coding foundations and your eagerness to apply them to gaming.

Review Your Past Projects

Be prepared to discuss your previous work in detail, including the challenges you faced and how you overcame them.

Ask Insightful Questions

Use the time at the end of the interview to ask about the team’s current technical challenges or their development culture.

Questions & practice

Can you explain the difference between pass-by-reference and pass-by-value?

Medium · Technical & Domain Knowledge

Approach

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

Follow-up

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

What is a dot product and what is it used for?

Medium · Mathematics & Performance

Approach

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

Follow-up

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

What is a cross product and how is it used in 3D space?

Medium · Mathematics & Performance

Approach

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

Follow-up

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

How do you identify and resolve performance bottlenecks in Unity?

Medium · Mathematics & Performance

Approach

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

Follow-up

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

Have you used the Unity Profiler to optimize a project?

Medium · Mathematics & Performance

Approach

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

Follow-up

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

Explain why the owner filter ignores the listing index

Medium · composite index · query plans · sort elimination

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

1. 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.
2. 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.
3. 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.
4. 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?

Keep soft-deleted accounts from blocking re-registration

Easy · soft delete · unique constraints · engine differences

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

1. 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.
2. 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.
3. 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.
4. 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?

What is the difference between a class and a struct in C#?

Medium · Technical & Domain Knowledge

Approach

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

Follow-up

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

What are the main differences between static and readonly keywords?

Medium · Technical & Domain Knowledge

Approach

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

Follow-up

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

How do you utilize Unity Coroutines, and what are their common pitfalls?

Medium · Technical & Domain Knowledge

Approach

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

Follow-up

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

What is the role of the camera in game development?

Medium · Technical & Domain Knowledge

Approach

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

Follow-up

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

How would you implement a game chest or reward system? What data structures would you select?

Medium · Game Systems & Architecture

Approach

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

Follow-up

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

Can you describe how to implement a match-3 mechanic or grid-based game logic?

Medium · Game Systems & Architecture

Approach

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

Follow-up

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

How would you implement a visual effect, such as an earthquake, within the game engine?

Medium · Game Systems & Architecture

Approach

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

Follow-up

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

What design patterns (e.g., Singleton) do you find most useful in game architecture?

Medium · Game Systems & Architecture

Approach

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

Follow-up

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

Listing latency scales with page size, not with filters

Easy · n+1 · latency · query batching

The tenant listing endpoint reads resource filtered by tenant_id and status, ordered by updated_at DESC, and returns each row plus the owner's display name from app_user and the actor of that resource's latest resource_revision. p99 is 55 ms at 10 rows per page and 1.4 s at 200. Database telemetry shows 401 statements per request, each under 1 ms, and nothing in the slow-query log. Diagnose the cause and give the fix, stating the statement count per request and the p99 you expect afterwards.

Approach

1. Read the counters before forming a theory. 401 statements for 200 rows is one driver query plus two per row, and sub-millisecond execution with an empty slow-query log rules out a bad plan. The time is round trips, which is why it is invisible in every per-query metric and scales with rows returned rather than with filter selectivity.
2. Name the two per-row statements from their normalised text: a single-row app_user lookup by user_id, and a resource_revision lookup by resource_id ordered by version DESC LIMIT 1. Confirm by dropping those two response fields and watching the statement count fall to one. That locates the calls in the serialisation layer, not the repository.
3. Check that the arithmetic accounts for the whole gap. Measure one round trip to the replica in isolation; 400 trips at roughly 3 ms of network plus 0.2 ms of execution is about 1.3 s on top of a 55 ms baseline, which matches. If the multiplication had fallen short, the N+1 would only be part of the story and you would keep looking.
4. Batch both lookups. Collect owner_user_ids and resource_ids from the driver query, then issue WHERE tenant_id = $1 AND user_id = ANY($2) for the users, and PostgreSQL's SELECT DISTINCT ON (resource_id) ... WHERE resource_id = ANY($2) ORDER BY resource_id, version DESC for the latest revision, which the UNIQUE (resource_id, version) index serves directly. On an engine without DISTINCT ON, use a lateral join or a row_number window. Three statements per request at any page size.

Follow-up

• The page size is capped at 200 today. What breaks first if it is raised to 2,000, and is it still this bug?
• How do you stop the next N+1 from reaching production, given that no individual query is slow and the endpoint's tests pass?

Suggested practice checklist

Built from the rounds and topics Jam City candidates report.

Day 1 — Map the Jam City loop

• Write out the reported sequence: Automated Test, Live Technical Interviews, Problem-Solving Assessment, Team Interaction, Cultural Fit Evaluation.
• 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.

Day 2 — Work Unity

• Spend the session on Unity, which Jam City candidates report being tested on.
• Write one worked example in Unity and time yourself on it.

Deliverable: One timed worked example in Unity.

Day 3 — Work C#

• Spend the session on C#, which Jam City candidates report being tested on.
• Write one worked example in C# and time yourself on it.

Deliverable: One timed worked example in C#.

Day 4 — Work Object-Oriented Programming (Classes/Structs)

• Spend the session on Object-Oriented Programming (Classes/Structs), which Jam City candidates report being tested on.
• Write one worked example in Object-Oriented Programming (Classes/Structs) and time yourself on it.

Deliverable: One timed worked example in Object-Oriented Programming (Classes/Structs).

Day 5 — Answer out loud: Technical & Domain Knowledge

• Answer aloud, timed: What is the difference between a class and a struct in C#?
• Answer aloud, timed: Can you explain the difference between pass-by-reference and pass-by-value?

Deliverable: Spoken answers to 2 reported Technical & Domain Knowledge question(s), under time.

Day 6 — Answer out loud: Game Systems & Architecture

• Answer aloud, timed: How would you implement a game chest or reward system? What data structures would you select?
• Answer aloud, timed: How do you handle game or player data storage using JSON?

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

Day 7 — Answer out loud: Mathematics & Performance

• Answer aloud, timed: What is a dot product and what is it used for?
• Answer aloud, timed: What is a cross product and how is it used in 3D space?

Deliverable: Spoken answers to 2 reported Mathematics & Performance question(s), under time.

Behavioural preparation

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

How do you handle game or player data storage using JSON?

Medium · Game Systems & Architecture

Approach

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

Follow-up

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

Can you walk us through a challenging technical situation you faced in a past project?

Medium · Behavioral & Experience

Approach

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

Follow-up

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

What is your favorite video game, and why?

Medium · Behavioral & Experience

Approach

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

Follow-up

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

How do you handle feedback from non-technical team members like producers or artists?

Medium · Behavioral & Experience

Approach

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

Follow-up

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

What is your experience working with Git and Agile development boards?

Medium · Behavioral & Experience

Approach

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

Follow-up

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