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First horizon bank Software Engineer Interview Guide

First horizon bank Software Engineer interview guide: reported rounds, questions and how candidates describe the process.

The 60-second brief

As a Software Engineer at First horizon bank, you are a critical contributor to the technological infrastructure that powers our financial services. You will be tasked with developing, maintaining, and scaling high-performance applications that serve a diverse client base. Your work directly impacts how our users interact with their financial data, ensuring security, reliability, and seamless performance in a highly regulated industry. This role requires a balance of technical precision and business acumen. You will not only write clean, efficient code but also collaborate with cross-functional teams to translate complex business requirements into robust software solutions. Whether you are working on internal tools or customer-facing platforms, your contributions will be vital to maintaining our competitive edge in the financial sector.

This guide is scoped to a Software Engineer candidate at First horizon bank.

Focus areas

Take-home coding assessment
Onsite follow-up interview
Communication skills (professionalism)

The First horizon bank interview process

First horizon bank candidates report 3 rounds over 3-5 weeks. The stages below are what candidates describe, not a published process.

Screening Call

Initial call from an HR representative to discuss your background, interest in the company, and logistical details.

What to demonstrate

Initial call from an HR representative to discuss your background, interest in the company, and logistical details
Depth in Take-home coding assessment

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

Includes a take-home coding assignment to evaluate your technical skills.

What to demonstrate

Includes a take-home coding assignment to evaluate your technical skills
Depth in Take-home coding assessment

How to prepare

Answer aloud and timed: How do you handle tight deadlines or shifting project requirements?
Answer aloud and timed: Why do you want to join the engineering team at First horizon bank?

Onsite/Virtual Interview

Meet with members of the engineering team to discuss your experience, technical approach, and cultural alignment.

What to demonstrate

Meet with members of the engineering team to discuss your experience, technical approach, and cultural alignment
Depth in Take-home coding assessment

How to prepare

Answer aloud and timed: Can you explain your approach to writing scalable and maintainable code?
Answer aloud and timed: How do you ensure the security of the applications you develop?

Where candidates lose points

Structure your answers

Use the STAR method (Situation, Task, Action, Result) for behavioral questions to keep your responses focused and impactful.

Prepare your own questions

Always have 3–5 thoughtful questions ready for your interviewers about the team’s current tech stack, the biggest challenges they are currently facing, or the company culture.

Be transparent about your experience

If you don't know an answer, it is better to explain how you would find the solution rather than guessing.

Mind your communication

In a professional environment like First horizon bank, your ability to communicate complex technical ideas to non-technical stakeholders is a significant advantage.

Questions & practice

Merge partitioned event streams into one ordered feed with bounded lateness

Hard · k-way merge · watermarks · out-of-order streams

The read-model service consumes 64 log partitions carrying about 4,000 events per second in total. Each partition is ordered within itself, but partitions drift by up to 30 seconds, and the activity feed must present a tenant's events in occurred_at order. Produce the merge. State its complexity, the buffer it requires in events and in bytes, what happens when one partition is idle, and what you do with an event that arrives after you have already emitted its position. Payloads average 1 KB.

Approach

Merge with a min-heap over the 64 partition heads keyed on (occurred_at, event_id): O(log P) per event and O(n log P) overall. The tie-break on event_id is what makes the output deterministic when two partitions carry the same millisecond, which matters because the feed is paginated and a non-deterministic order reorders pages under the reader.
Emitting the heap head is only correct once every partition has produced everything up to that timestamp, so the emit condition is a watermark: the minimum across partitions of the highest occurred_at seen, less the allowed lateness. Events are held until the watermark passes them, which is what turns individually ordered streams into a jointly ordered one.
Size the buffer from the lateness rather than guessing: 4,000 events per second times 30 seconds is 120,000 buffered events, and at 1 KB each about 120 MB of heap. That number is the real price of the ordering guarantee and belongs in front of whoever asked for it.
Handle the idle partition explicitly, because it fails the feed rather than corrupting it: a partition with no traffic never advances its own maximum, so the watermark freezes and output stops entirely. Either every partition emits a periodic idle marker carrying the broker's current time, or the watermark falls back to wall clock for a partition silent beyond a threshold.

Follow-up

The lateness budget is raised to five minutes. What is the new buffer, and what besides memory changes?
The consumer restarts. Where does it resume from, and what does the feed look like for the first 30 seconds?

Collapse a redelivered event batch into per-aggregate high-water marks

Easy · hashing · at-least-once · aggregation

You drain a batch of up to 5,000,000 events, each (aggregate_id BIGINT, aggregate_version INT, event_type, payload). The log guarantees order within one aggregate only; the batch merges 64 partitions, and a relay failover has redelivered a range, so an older version for an aggregate can appear after a newer one. Given a map of last_applied_version per aggregate, produce the events worth applying, at most one per (aggregate_id, version), plus the count discarded. Target O(n) time. State the memory for 2,000,000 distinct aggregates and what you do when it does not fit.

Approach

One pass, one hash map from aggregate_id to the highest version kept, and a discard counter. An event whose version is at or below last_applied_version for its aggregate is dropped without further work, which is the whole reason the event carries its version rather than a delta. O(n) expected time, O(d) space in distinct aggregates.
Keep the maximum, never the last occurrence. The redelivered range means the final appearance of an aggregate in the batch can be an older version than one seen earlier in the same batch, so last-wins applies stale state over newer state and the projection regresses with no error anywhere.
Cost the memory instead of calling it large: an 8-byte key plus a 4-byte version is 12 bytes of payload, and an open-addressed table held at a 0.7 load factor costs roughly 17 bytes per entry before per-slot metadata, so 2,000,000 aggregates is tens of megabytes in a native layout and several times that in a runtime that boxes both key and value.
If the distinct set exceeds memory, partition on hash(aggregate_id) mod P and reduce each partition independently. Every event for one aggregate hashes to the same partition, so the per-partition result is exact and the merge is concatenation rather than a second reduction.

Follow-up

The payload is a patch rather than a snapshot, so applying only the highest version loses the intermediate changes. What changes in your reduction?
How do you detect that version 7 arrived while version 6 was never delivered, and what should the consumer do about the gap?

Canonicalise a request body into a stable idempotency fingerprint

Medium · parsing · canonicalisation · hashing

idempotency_key.request_fingerprint is a SHA-256 over the method, path and canonicalised body, and a retry whose fingerprint differs must be rejected with 422 rather than served the stored response. Write the canonicaliser. Bodies are JSON up to 256 KB nested at most 32 levels; clients vary key order, whitespace and unicode escaping, and some send 64-bit ids as JSON numbers. Produce a deterministic byte string such that semantically identical bodies match and any semantic difference does not. State your complexity and name two normalisations you refuse to perform.

Approach

Parse once into a tree, then re-serialise under fixed rules: object keys sorted, array order preserved, one escaping convention, no insignificant whitespace. Parsing is O(n) and sorting keys is O(k log k) per object, so O(n log n) overall with O(depth) stack, and the 32-level cap is enforced during parsing because hostile nesting is how a canonicaliser becomes a stack overflow.
Sort keys by their UTF-8 bytes and say why the obvious implementation is wrong in some runtimes: a default string comparison that orders by UTF-16 code units places surrogate pairs, meaning code points from U+10000 up, below U+E000 to U+FFFF, which is not UTF-8 byte order, so two services written in different languages disagree on the same document.
Do not re-encode numbers through a double. IEEE-754 binary64 represents integers exactly only up to 2^53, so normalising a 19-digit id through a float changes it, and 1 against 1.0 cannot be reconciled without deciding whether they are the same value. Preserve the literal token, and require ids as strings at the API boundary if you want them comparable.
Reject duplicate keys rather than picking one. JSON permits them and parsers disagree, most keeping the last, so any choice you make ties the fingerprint to a parser detail that the code handling the request does not necessarily share.

Follow-up

A client sends the same logical request with an extra field your API ignores. Same key, different fingerprint, so you return 422. Is that the right answer?
Where does the fingerprint get computed relative to request decompression and the body-size limit?

Why do you want to join the engineering team at First horizon bank?

Medium · Experience and Background

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?

If you were tasked with optimizing a slow-performing database query, what steps would you take?

Medium · Problem-Solving and Logic

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?

Can you walk me through your previous projects and your specific role in them?

Medium · Experience and Background

Approach

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

Follow-up

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

What are the most significant technical challenges you have faced in your career?

Medium · Experience and Background

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 your approach to writing scalable and maintainable code?

Medium · Technical and Domain Knowledge

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 do you ensure the security of the applications you develop?

Medium · Technical and Domain Knowledge

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 system to handle high-frequency transaction data?

Medium · Problem-Solving and Logic

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 do you approach debugging complex issues in a production environment?

Medium · Technical and Domain Knowledge

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?

Suggested practice checklist

Built from the rounds and topics First horizon bank candidates report.

Day 1 — Map the First horizon bank loop

Write out the reported sequence: Screening Call, Technical Assessments, Onsite/Virtual Interview.
For each round, write one sentence on what it is judging, from the description above, and mark the one you are least ready for.

Deliverable: A one-page map of the 3 reported rounds, with the weakest marked.

Day 2 — Work Take-home coding assessment

Spend the session on Take-home coding assessment, which First horizon bank candidates report being tested on.
Write one worked example in Take-home coding assessment and time yourself on it.

Deliverable: One timed worked example in Take-home coding assessment.

Day 3 — Work Onsite follow-up interview

Spend the session on Onsite follow-up interview, which First horizon bank candidates report being tested on.
Write one worked example in Onsite follow-up interview and time yourself on it.

Deliverable: One timed worked example in Onsite follow-up interview.

Day 4 — Work Communication skills (professionalism)

Spend the session on Communication skills (professionalism), which First horizon bank candidates report being tested on.
Write one worked example in Communication skills (professionalism) and time yourself on it.

Deliverable: One timed worked example in Communication skills (professionalism).

Day 5 — Answer out loud: Experience and Background

Answer aloud, timed: Can you walk me through your previous projects and your specific role in them?
Answer aloud, timed: What are the most significant technical challenges you have faced in your career?

Deliverable: Spoken answers to 2 reported Experience and Background question(s), under time.

Day 6 — Answer out loud: Technical and Domain Knowledge

Answer aloud, timed: Can you explain your approach to writing scalable and maintainable code?
Answer aloud, timed: How do you ensure the security of the applications you develop?

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

Day 7 — Answer out loud: Problem-Solving and Logic

Answer aloud, timed: How would you design a system to handle high-frequency transaction data?
Answer aloud, timed: If you were tasked with optimizing a slow-performing database query, what steps would you take?

Deliverable: Spoken answers to 2 reported Problem-Solving and Logic question(s), under time.

Behavioural preparation

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

How do you handle tight deadlines or shifting project requirements?

Medium · Experience and Background

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 experience with the specific tech stack we use?

Medium · Technical and Domain Knowledge

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 you had to learn a new technology quickly to finish a project.

Medium · Problem-Solving and Logic

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?